ATLANTA -- Twelve nations, including Canada, have reached a tentative deal on a massive Pacific Rim trading bloc billed as the largest-ever deal of its kind, with implications for a staggering scope of industries, workers, and for long-term international relations between countries on four continents.

After five days of marathon, around-the-clock negotiations, a deal was announced Monday to create the Trans-Pacific Partnership -- which would cover 40 per cent of the world's economy, for starters, and participants predicted it would become the building block for future trade deals.

"Today is a historic day; it is a great day for Canada, it is a great day for Canadians," Prime Minister Stephen Harper beamed during a news conference Monday in Ottawa.

"With this agreement, the largest economic partnership in the history of the world, Canadian exporters will gain nearly tariff-free access to almost 800 million customers in the Asia-Pacific region... including -- crucially for us -- Japan."

First, however, the deal requires political approval.

To take effect, the deal must be ratified by the parliaments and lawmaking authorities of all 12 member countries. Canada will be the first political testing-ground -- the agreement lands smack in the midst of a federal election campaign that will decide who will control the Parliament that determines whether it lives or dies.

The drama reached a high point overnight Monday, as a series of delays culminated in an agreement around 5 a.m. on a persistent irritant involving dairy and the future of Canada's tightly controlled sector.

The Canadian government appears to have guaranteed the long-term entrenchment of the supply-managed sector, which is detested by free-market economists but backed by every major political party, provincial governments, and the domestic dairy lobby.

Canada agreed to 3.25 per cent more foreign imports, a minuscule change compared to what some countries asked for. That means a bit more international products like butter on grocery shelves now 90-per-cent dominated by domestic content. For their loss, the government would compensate Canadian farmers billions of dollars under a series of programs over at least 10 years.

It's a little less clear what impact the deal might have on the auto sector.

The agreement would allow a 17.5 per cent greater tariff-free share of cheaper intercontinental parts compared to the standard set out in NAFTA, although the formula is apparently complex and includes a series of exemptions. New measures to attract auto investment and protect auto-assembly operations in Canada will be forthcoming shortly, Harper added.

The Canadian envoy to the talks didn't make any promises specific to workers in any individual sector. But he appeared to insist there would be no net negative impact on Canadian employment as a whole.

"We certainly don't anticipate that there will be job losses," said International Trade Minister Ed Fast, who suspended his re-election campaign in B.C. for nearly a week to attend the Atlanta talks.

"Obviously there will be some industries that will adapt."

His New Zealand counterpart Tim Groser had expressed some disappointment earlier this week. In an apparent reference to the smaller-than-hoped-for concessions in dairy, he said completing a deal would require every country to take a deep gulp and swallow a few "dead rats."

But Groser predicted Monday that the agreement would have far-reaching geopolitical benefits.

"Long after the details of this negotiation on things like tonnes of butter have been regarded as a footnote in history, the bigger picture of what we've achieved here remains," Groser said.

"It is inconceivable that the TPP bus will stop in Atlanta. The TPP bus will move on."

Several countries including Thailand and Colombia have already mused about joining TPP, which involves North America, Chile, Peru, Japan, Brunei, Singapore, Vietnam, Malaysia, New Zealand and Australia.

The proposed agreement reduces or eliminates barriers in a wide range of sectors and could lead to more Canadian exports of pork, beef, canola, high-tech machinery and a variety of other products.

As one example among hundreds, the beef industry predicts exports to Japan will triple. The 39 per cent current tariff in Japan will become nine per cent over the next few years, and barriers will completely disappear in other areas.

But voters can't yet see the fine print.

The actual text of the deal is undergoing a legal review, and it's not clear when it will be available. The government offered no guarantees at a news conference. It simply expressed hope the 12 countries might manage to make it available in the next few days -- before voters pick a government Oct. 19.

Some members of Canada's auto sector reacted with consternation, eager to see the details. A coalition of Canadian unions called it a serious blunder -- the result of myriad consultations with multinational corporations and lobbyists in a process that excluded labour and civil society.

But the dairy farmers started celebrating quickly.

The supply-management system appears assured for at least another generation, said the head of Dairy Farmers of Canada. It's now survived two big international trade negotiations, including the one with Europe. And with no other big deals on the horizon, it appears the system of quotas and import controls is here to stay.

"The TPP is good for Canada," said Wally Smith.

"'Farmers today in Canada are far more confident in their future... as opposed to always having a cloud over their head."

Here are 10 questions about the Trans-Pacific Partnership, answered:

Who's in it? Brunei, Chile, New Zealand and Singapore started the project years ago. The United States, Canada, Mexico, Japan, Vietnam, Australia, Peru and Malaysia are now joining, bringing the membership to 12 countries. More have expressed interest in entering later, including Colombia, Thailand and South Korea.

How big is it? It's the biggest trade zone in the world, spanning four continents and representing 40 per cent of the world's economy -- a far higher share than the European Union.

Is it more important than the EU? Not even close. Europe has truly open borders, allowing a free flow of people and products from one country to another. This simply changes regulations, and reduces trade barriers across a larger area.

What does it do, then? It reduces or eliminates barriers on a staggering array of Canadian exports to several countries, most notably Japan. This applies to everything from machines to canola, beef and pork, minerals, forestry products and seafood. It allows up to 3.25 per cent more foreign dairy into Canada. It allows more foreign car parts into North America without tariffs. It also creates new rules for the digital economy, such as restricting governments' right to shut off data flows.

Why does it matter? This brings the economies of a fast-developing region into the American sphere of influence. It sets new trade standards in China's backyard. It sets precedents for future agreements, including any involving China and its state-owned-enterprises. It increases trade and establishes unique rules for the 21st-century, cloud-computing digital economy.

So what's the problem? It also exposes middle-class workers to additional low-cost competition from foreign labour, notably in the auto sector. It would also cut into the profits on dairy farms, although the government promises a multibillion-dollar 10-year program to protect current farm revenues. Government decisions could be overturned in special tribunals, as they are in NAFTA, when companies sue over democratically adopted laws.

Is it a done deal? No. It still needs to be ratified in national parliaments, including Canada's, once the federal election is over. A vote is expected early next year in the U.S. Congress, and it could prove difficult.

So can we see the full text? No, not yet. It's undergoing a legal review. The details that have been released are coming from the various governments. One Canadian official expressed hope the parties would manage to release the agreement within a few days. But it's unclear whether Canadians will get to see it before they vote on Oct. 19.

Does this end NAFTA? No. The North American Free Trade Agreement still exists, but in areas where the two agreements conflict the newer one will usually prevail. In a way, this is what Barack Obama promised when he first ran for president and said he'd revisit NAFTA -- which prompted a controversy back in 2008. He promised new labour and environmental provisions, and this agreement has chapters on both those things.

Does this end Canada Post and the CBC? No. There's a popular online theory to that effect, based on the provisions limiting the rights of state-owned-enterprises. But the government insists the relevant chapter excludes public services, and specifically says the CBC and Canada Post won't be touched.