Larry Kudlow said Mr. Trump negotiated in good faith with fellow global powers in Quebec.
The stunning remarks widened a rift on trade policy between the United States and Canada, which has joined the European Union and Mexico in blasting Trump's decision to impose tariffs on imports of steel and aluminum.
It was unclear why Trump and his aides have suddenly begun speaking of Trudeau this way.
White House trade adviser Peter Navarro went a step further, suggesting to Fox News Sunday morning that there's a "special place in hell" for the Canadian prime minister. Japanese Prime Minister Shinzo Abe - a veteran of seven G7 leaders' meetings - said the Charlevoix summit featured heated exchanges, the likes of which he has never seen.
But "at the same time we need to avoid tit-for-tat escalation" and maintain a constructive dialogue, she said.
At a Saturday afternoon press conference in La Malbaie, he blamed Barack Obama for the Russian invasion of Ukraine and complained about the USA being a "piggy bank" which he said other countries were "robbing".
Trudeau told the president that Canadians did not take it lightly that the US has moved forward with significant tariffs on their steel and aluminum industry. He justified President Trump's decision to drop out of a joint statement made by G7 countries this weekend.
"These are jointly shared principles, although the pitfalls lie in the details", she said in a press conference, adding that she expected a joint G7 statement on trade would be issued at the end of the summit. "He did him a favor and he was even willing to sign that socialist communique and what did Trudeau do as soon as the plane took off from Canadian airspace?"
Kudlow lashed out at Trudeau first during an appearance on CNN's "State of the Union".
The US president's Twitter feed carried a video of his press conference before leaving the G7 meeting.
He was reacting to Trudeau's declaration that Canadians would "not be pushed around" and would hit back at punishing United States tariffs on metal imports with "equivalent tariffs".
A spokesman for German Chancellor Angela Merkel said the other G7 members stand by the communique and all that was agreed upon.
"Is that really how we want to deal with our second-biggest trading partner?"
He said Trump "did the courtesy to Justin Trudeau to travel up to Quebec for that summit".
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He instructed USA representatives not to sign the communique from the summit, raising new questions about Mr. Trump's strained relationship with leaders of historic allies.
But Kudlow said he doesn't know whether there will be a deal and that Trump had no alternative but to respond the way he did to Trudeau's "very unfortunate" statements.
European officials said Mr Trump had tried to water down the language in the draft communique on the WTO and rules-based trade. Without naming the president in his tweet, Comey said that the country's relationship with Canada is crucial for national security.