OTTAWA -- With the possibility Canada could join a massive Pacific Rim trade deal within hours, Tom Mulcair tried to cast his NDP on Sunday as the only party ready to stand up to the Conservatives on a pact he insisted could hurt Canadian farmers and manufacturers.

"The NDP, when we form government on Oct. 19, will not be bound by this secret agreement that Mr. Harper has been negotiating," the NDP leader said at a campaign stop in Brantford, Ont.

Mulcair made the comments as his campaign rolled across southwestern Ontario with half a dozen planned stops, including the cities of London and Sarnia.

While in Waterloo, Mulcair warned a crowd of 300 of what the controversial, 12-country Trans-Pacific Partnership could do to the region's farmers.

"Think about the family that's been running that dairy farm for generations," he said.

His whistle-stop tour took place as negotiators in Atlanta tried to seal the deal on a long-awaited agreement. A briefing about the deal was scheduled for later in the day in Ottawa.

In an effort to conclude the agreement, negotiators held a series of all-night sessions pushing the meeting three days beyond its original schedule.

Mulcair has been trying to burnish his social-democratic credentials by insisting he won't be bound by a Conservative deal on the Trans-Pacific Partnership, which would create the world's largest trade zone.

It remains to be seen whether Mulcair's blitz would jump-start the NDP campaign, which recent polls suggest has been stalling.

Mulcair has hammered away on the importance of upholding the country's supply management system for dairy and poultry farmers.

Foreign negotiators have said Canada's protectionist system would have to be opened up for a deal to be reached, though it remains unclear what concessions might be made by the federal government.

The Conservatives have insisted they would keep the supply-management system intact amid political pressure from opponents, provincial governments and the dairy lobby.

But the federal government has left open the possibility it could allow for an additional, if limited, share of foreign goods into Canadian grocery stores.

A TPP deal, which the government has said would boost the Canadian economy as a whole, could also have a similar effect on the auto sector.

Later Sunday, Liberal Leader Justin Trudeau was scheduled to headline what the party has billed as the biggest rally of the campaign -- at a hall in Brampton, Ont., that seats up to 5,000 people.

Conservative Leader Stephen Harper had no scheduled public campaign events Sunday.

But Canadians could hear from Harper if the high-level meetings in Atlanta produce a deal that his Tories would certainly try to sell as further evidence they are good economic managers.

Green party Leader Elizabeth May was scheduled to campaign Sunday in Victoria, where she was expected to announce her plan for arts and culture.