Canadian Foreign Minister Chrystia Freeland has said she remains "optimistic" that she can reach a deal with the United States by tomorrow to revise the North American Free Trade Agreement.

"There's a lot of goodwill on both sides," she told reporters today after another meeting with US Trade Representative Robert Lighthizer.

"I continue to be optimistic," she said when asked if a deal was possible by the end of the week.

Earlier, US President Donald Trump and Canadian Prime Minister Justin Trudeau expressed optimism that they could reach a new NAFTA by tomorrow's deadline.

Under pressure, Canada rejoined the talks to modernise the 24-year-old NAFTA after Mexico and the United States announced a bilateral deal on Monday.

President Trump set the deadline for the three countries to reach an in-principle agreement, which would allow Mexican President Enrique Pena Nieto to sign it before he leaves office at the end of November.

Under US law, Mr Trump must wait 90 days before signing the pact.

He has warned he could try to proceed with a deal with Mexico alone and levy tariffs on Canadian-made cars if Ottawa does not come on board, although US legislators have said ratifying a bilateral deal would not be easy.

"They (Canada) want to be part of the deal, and we gave until Friday and I think we’re probably on track. We’ll see what happens, but in any event, things are working out very well." Mr Trump told reporters at the White House.

The upbeat tone contrasted with President Trump’s harsh criticism of Canada in recent weeks, railing on Twitter against Canada’s high dairy tariffs that he said were "killing our Agriculture!"

Mr Trudeau said he thought the Friday deadline could be met.

"We recognise that there is a possibility of getting there by Friday, but it is only a possibility, because it will hinge on whether or not there is ultimately a good deal for Canada," he said at a news conference in Ontario yesterday.

"No NAFTA deal is better than a bad NAFTA deal."

Ms Freeland, who is Canada’s lead negotiator, was sidelined from the talks for more than two months, and will be under pressure to accept the terms the US and Mexico worked out.

She declined comment on the issues still in play, but said on Tuesday that Mexico’s concessions on car rules of origin and labour rights had been a breakthrough.