He said trade practices of many countries are very unfair to USA farmers.
The President warned Canada and Europe to back off their threats to hit back with retaliatory trade measures on July 1 if the US does not lift the steel and aluminum levies.
In her own tweet, Green Party leader Elizabeth May says Trudeau is handling what she calls Trump's outbursts and bullying as well as anyone, and that all Canadian leaders need to support the prime minister. He added that the USA will take the necessary steps to protect industry and workers from unfair practices.
The sides had managed to eke out a compromise final summit statement that pledged to protect the worldwide rules-based order and reform the trade system.
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.
With Trudeau, Trump joked that "Justin has agreed to cut all tariffs and all trade barriers between Canada and the United States".
LA MALBAIE, Quebec: U.S. President Donald Trump on Saturday accused other countries of "robbing" the United States on trade and threatened to stop doing business with them altogether as he pushed his "America First" agenda at a Group of Seven nations summit.
But Mr Trump insisted it would be an "asset" to have Vladimir Putin back at the summit table.
President Donald Trump left the G7 talks early, flying directly to Singapore to meet with North Korean leader Kim Jong Un.
"The European Union is brutal to the United States and they know it", Trump said, adding that other leaders acknowledge as much in private.
He said retaliatory measures against the USA would come into place on July 1, even though it was "not something we want to do".
The G7 joint communique, which advocates a "rules-based trading system", was reached despite tension over USA tariffs on steel and aluminium imports, reported BBC.
Although Canada and Mexico say the idea is unworkable, Trump told reporters earlier on Saturday that the new deal would contain such a provision. A flummoxed spokesman said Mr Trudeau had said nothing at the news conference he had not already said before to Mr Trump, both publicly and privately.
Leading up to the meetings, Trump, Trudeau and French President Emmanuel Macron had suggested the potential for a tough tone, though they were cordial in face-to-face meetings.
Trump had grumbled to aides ahead of the meeting that he didn't want to go sit through lectures from the other leaders, and he mused about sending Vice President Mike Pence in his place.
"I wasn't sure - he said it so beautifully". In fact, Russian Federation was expelled from what was then the G-8 after it invaded and annexed Crimea and for its support for pro-Russia separatists in Ukraine.
"He is not going to permit any show of weakness on the trip to negotiate with North Korea", Kudlow said.
The president also referred to Trudeau's "false statements", which he didn't explain. It could also cause fresh friction with his northern neighbour as tensions percolate over efforts to redraw the North American Free Trade Agreement.
Despite the sharp differences, Trudeau said all seven leaders had come together to sign a joint declaration despite having "some strong, firm conversations on trade, and specifically on American tariffs". "And I don't blame other leaders for that".