"And I highlighted it was not helping in our renegotiation of NAFTA and that it would be with regret but it would be with absolute certainty and firmness that we move forward with retaliatory measures on 1 July - applying equivalent tariffs to the ones that the Americans have unjustly applied to us".
The prospect that he could be moving toward an even greater protectionist trade policy is likely to chill financial markets anxious about tit-for-tit escalation that could lead to a full-blown global trade war.
"We're either going to have NAFTA in a better negotiated form or we're going to have two deals", the USA president said.
At the summit, Trump played a wild card, suggesting that rather than both sides boosting retaliatory tariffs - as he has just done on steel and aluminum - they could declare for entirely free trade in the G7 zone. That's the way it should be. On Friday, Mr Trump made a surprise call for Moscow to be readmitted, but German Chancellor Angela Merkel said other members were against the idea.
Trump has announced tariffs of up to $150 billion on Chinese goods over US complaints of Beijing's trade practices and its alleged theft of USA technology.
Theresa May went on to warn the loss of trade through tariffs "ultimately makes everyone poorer".
Over the course of the summit, the President pushed the narrative that the U.S.is a victim of a trade imbalance, though European leaders rejected these claims. "They know it", he insisted in his departing news conference.
'I think there are various discussions about alternatives that would not be that, and that would not be entirely destabilizing for a trade deal, and I think we are open to creativity, ' he said. "It's going to stop".
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It is an annual summit bringing together Canada, the USA, the UK, France, Italy, Japan and Germany, which represent more than 60% of global net worth between them. And that's a very profitable answer, if we have to do it.
"The United States has been taken advantage of for decades and decades", Trump said.
"This has been the most awkward G7 meeting in it's 43 years of history and it's due to Trump's behaviour" says Keith Suter.
Whatever the text eventually says, Canada's summit will be remembered mainly for fierce disagreements over Trump's tariffs and his surprise request to return Russian Federation to the G7 fold, four years after its expulsion over the annexation of Crimea.
Canadian Prime Minister Justin Trudeau addresses a press conference at the conclusion of the G7 summit in La Malbaie, Quebec, June 9, 2018. Trump arrived 17 minutes after the planned 8:00am start time and after Trudeau's opening remarks. Bannon said China is "now on notice that Trump will not back down from even allies" complaints in his goal of "America First'".
He also denied the summit had been contentious, a remark that contradicted what one G7 official described as an "extraordinary" exchange on Friday in which Trump repeated a list of trade grievances, mainly concerning the European Union and Canada.
Vice President Mike Pence told Trudeau he would have to agree to that before Trump would agree to meet him.