The spat has also drawn in Germany and France, who sharply criticised Mr Trump's decision to abruptly withdraw his support for a G7 communique hammered out at a Canadian summit, accusing him of destroying trust and acting inconsistently.
US President Donald Trump has imposed a 25 per cent tariff on import of steel from Canada and another 15 per cent on aluminium using the "national security interest" provisions of the existing American laws. "American lawmakers and USA allies strongly oppose Trump's erratic behaviour against their biggest and closest friend", said NDP House Leader Ruth Ellen Brosseau. "We make our commitments and keep them".
Tensions have been building between the two countries for months, as President Trump has targeted Canada as one of the many countries he sees as giving American the short end of the stick in trade deals.
In response to Mr Trump's decision to withhold United States support for the summit conclusions, a senior United Kingdom government source said: "We stand by the commitments made in the G7 communique".
While the agreement of legislators who are normally opposed on most fronts was remarkable, the anger also spread to pundits, officials, celebrities and ordinary citizens as Canadians vowed consumer boycotts of American goods and brainstormed insults of Trump on social media.
Of the 32 states that count Canada as their biggest export destination, 20 voted for Trump in the 2016 election.
After the G-7 summit, Trudeau hosted a news conference where he said that the Canadian government "did not take" the USA tariffs against Canada lightly. According to Trudeau, he told the president that Canadians may be polite and reasonable but they will not be pushed around and that his nation doesn't "relish" putting tariffs on US goods and services but is willing to do so. "Minimum is 17B. Tax Dairy from us at 270%", he wrote in the first of five tweets relating to the weekend's summit. These are the kinds of things that are common challenges across our countries and around the world where anxiety about economic prospects of individuals and particularly of their kids leads to unpredictability and sometimes political uncertainty.
Trudeau was quick with his riposte: "So I'd say NAFTA is in good shape".
"PM Justin Trudeau of Canada acted so meek and mild during our G7 meetings only to give a news conference after I left saying that, "US Tariffs were kind of insulting" and he 'will not be pushed around.' Very dishonest & weak", tweeted Trump.
So what exactly did Trudeau say? I mean, it's not a question of 'I hope it changes.' It's going to change, a hundred percent.
"Fair Trade is now to be called Fool Trade if it is not Reciprocal", Trump tweeted, as he criticised Canadian tariffs on imports of U.S. milk.
He concluded: "Sorry, we can not let our friends, or enemies, take advantage of us on Trade anymore".
"The reactions from White House Trade Czar Peter Navarro and NEC Director Larry Kudlow are so outsized it would seem that Trump himself was apoplectic when he heard/saw the comments from Prime Minister Justin Trudeau and that Navarro and Kudlow were speaking to an audience of one on instruction", he said.