OTTAWA – U.S. President Donald Trump on Friday criticized Canada for being "highly restrictive on trade,” then suggested replacing NAFTA with separate deals for his northern neighbour and Mexico, as Canada filed a legal challenge over steel and aluminum tariffs.

In a 274-character tweet, Trump implored Canada to open its markets and take down its trade barriers.

"Canada has treated our Agricultural business and Farmers very poorly for a very long period of time. Highly restrictive on Trade! They must open their markets and take down their trade barriers! They report a really high surplus on trade with us. Do Timber & Lumber in U.S.?" he tweeted.

In reality, the U.S. government, by its own account, reported a U.S. goods and services trade surplus of US$8.4 billion with Canada in 2017.

Trump's tweet comes a day after the U.S. levelled steel and aluminum tariffs on Canada, among other countries, and Ottawa retaliated with its own dollar-for-dollar countermeasures, including new taxes on steel, aluminum, and various other American products.

Canada has filed a legal challenge against the tariffs with the World Trade Organization, joining the European Union.

“These unilateral tariffs, imposed under a false pretext of safeguarding U.S. national security, are inconsistent with the United States’ international trade obligations and WTO rules,” Foreign Affairs Minister Chrystia Freeland said in a statement.

The tariffs have put serious doubts on whether Canada, the U.S. and Mexico can bring the current NAFTA talks to a successful close.

Those doubts were further amplified Friday as Trump openly suggested separate deals.

"To be honest with you, I wouldn't mind seeing NAFTA where you'd go by a different name where you make a separate deal with Canada and a separate deal with Mexico," he said at the White House.

Canada has responded to the steel and aluminum tariffs with $16.6 billion in planned countermeasures, which includes surtaxes aimed to hit major industries in some high-profile Republican districts, such as gherkins from Republican House Speaker Paul Ryan's Wisconsin stomping ground, and whiskies from Senate Majority Leader Mitch McConnell's home state of Kentucky.

In announcing the retaliatory measures, Prime Minister Justin Trudeau called it "a turning point in the Canada-U.S. relationship," and expressed hope that "common sense" will prevail, despite seeing no sign of it from the U.S. administration.

Speaking to reporters on her way into question period on Friday, Freeland didn’t comment on Trump’s tweet, but said she’s heard from many Canadians in the last 24 hours that back the federal government’s position.

“This is a moment when it is important for us to be clear and firm,” Freeland said.

Public Safety Minister Ralph Goodale also remarked on the subject as he made his way into the House. He said he hasn’t had the opportunity to reach out to Trump’s chief of staff John Kelly, who he developed a relationship with when Kelly was Secretary of Homeland Security, since the tariffs were announced.

“We’ll be pursuing every particular avenue to point out that this is not just damaging to Canadians, it damages the United States,” he said. “American consumers will end up paying much, much more and it will be entirely counterproductive for the U.S. economy.”

In an interview on BNN, former Conservative foreign affairs minister Peter MacKay said that the exchange of words and trade action yesterday puts “a lot of ice under the relationship.”

MacKay said that like with any war, there will be collateral damage, and classified this week’s events as “friendly fire.”

“Now we’re into an era where the United States, as has been aptly said before, has no friends and enemies, only interests and that creates such uncertainty and volatility across so many markets,” MacKay said.