Canada will continue to be in a trade war with the United States for the foreseeable future, Prime Minister Justin Trudeau said on Thursday, a day after what he called a "colorful" call with President Donald Trump.

Trudeau said Canada would continue to engage with senior Trump administration officials about tariffs Washington says it will impose on Canadian imports, reiterating that his goal was to get the measures removed.

"I can confirm that we will continue to be in a trade war that was launched by the United States for the foreseeable future," he told reporters in Ottawa.

Canada immediately imposed 25% tariffs on C$30 billion of U.S. imports and Trudeau said those measures would remain in place until the Trump administration ended its trade action.

Trudeau and Trump, who accuses Canada of not doing enough to stop the flow of fentanyl and illegal migrants across the border, held a 50-minute call on Wednesday.

"It was a colorful call. It was also a very substantive call," said Trudeau, adding that the two sides were in talks but had nothing to announce yet.

"We are ... trying to make sure that these tariffs don't overly harm, certainly in the short term, certain sectors."

One topic of conversation is Canada possibly delaying a second round of 25% tariffs on a further C$125 billion of U.S. imports, due to come into effect in less than three weeks.

Trump will exempt automakers from tariffs on Canada and Mexico for one month as long as they comply with existing free trade rules, the White House said on Wednesday.

"Any carve outs that support any workers in Canada, even if it's just one industry or another, are going to be a good thing," said Trudeau.

The Canadian prime minister will step down once the ruling Liberal Party chooses a new leader this Sunday. He has generally had poor relations with Trump and took a swipe at the president, who first made a name for himself as a real estate mogul.

"A win-lose between us would actually be worse for them than a win-win. That's true in international trade, in relations between nation states," he said.

"It perhaps is not true in real estate deals, (where) a win-lose is probably better for someone who is experienced in business deals than a win-win," he said.