The next federal election will formally begin Wednesday morning with a trip by Prime Minister Justin Trudeau to Rideau Hall, where he'll ask Gov. Gen. Julie Payette to dissolve Parliament, according to Liberal sources who agreed on condition of anonymity to confirm details not yet released to the public.

With that starts five weeks of cross-country campaigning in earnest by the leaders of the federal parties vying to form government when Canadians cast their ballots Oct. 21.

All have effectively been campaigning for weeks, setting the stage for what many predict will be a brutish battle for the 170 seats needed for a majority.

Liberal ministers have been making government funding announcements all summer long, while at the same time rarely missing an opportunity to swipe at their chief rivals, the Conservatives, for their links to some of the more polarizing figures on the political right. The Conservatives and New Democrats bounced around the country too, taking turns bashing the Liberal record while hyping their own bona fides.

In Quebec, a major battleground with 78 seats, the Bloc Quebecois aren't just going after the Liberals but at Green Leader Elizabeth May, whom they view as a potential threat in their backyard. May's party heads into this election in one of its strongest positions ever and she's spent the summer shoring up the national campaign.

Trying to prove he also has one of those is People's Party of Canada chief Maxime Bernier, the former Tory now stirring the political pot with controversial positions on immigration and climate change, and fighting a battle to be included in the official election debates scheduled for the second week of October.

Key themes this election will likely include environmental policy, Canada's place in the world, federal spending, and to what extent a national economy that has performed well by statistical measures has secured Canadians' personal finances.

That last point will be central, with the three main federal parties all promising to make life in Canada more affordable.

Both the Conservatives and New Democrats have already started making campaign promises in that spirit.

The Conservatives have pledged, among other things, to cut the federal tax on home-heating bills. Just Tuesday, the NDP promised a tax on the super-rich to fund expanded public health coverage.

"New Democrats have the courage to make different choices. Unlike the Liberals and Conservatives who work for their rich and powerful friends, we will help people who are struggling to get by," said NDP Leader Jagmeet Singh in Hamilton, Ont.

"Our plan is simple -- we can afford to help people when we have the courage to ask the super-rich to pay a little bit more to fund the services we all rely on."

Except to see a lot of Singh in the Hamilton area. The NDP is faltering in the polls nationally but believe that's one zone where they won't just hold onto seats but potentially pick up one or two, thanks to union card holders frustrated by the Liberals.

But the election begins Wednesday with the Liberals and Conservatives duelling for first place in popular support. Polls suggest at this point, neither would likely win a majority in the House of Commons if an election were held immediately. At least 170 seats are required to form a majority government.

Heading into the election, the Liberals hold 177, the Conservatives 95, the NDP 39, the Bloc 10 and the Greens 2. There are eight independents -- including former Liberal cabinet ministers Jane Philpott and Jody Wilson-Raybould. The People's Party of Canada has one seat and former New Democrat Erin Weir sits as a member of the Co-operative Commonwealth Federation. Five seats are vacant.

By law, voting day is set for Oct. 21, but the prime minister had a two-week window starting Sept. 1 in which to begin the formal campaign.

The opposition parties, which have been highly critical of the Liberals' summer spending spree, had already decided to just kick off their own efforts. The NDP's campaign began over the weekend, while the Greens and the Conservatives will also begin Wednesday.

Conservative Leader Andrew Scheer starts at an event in Trois-Rivieres, Que., before moving on to an evening rally in a riding just outside Toronto.

"Canada's Conservatives have been ready to go for months," said spokesman Simon Jefferies.

"We have all of our candidates nominated. We have been breaking fundraising records. Our local campaigns are energized with volunteers."