Trudeau joined Trump in the Oval Office at the start of a new round of talks over the North American Free Trade Agreement, which the US president has threatened to withdraw from if he can't negotiate a better agreement with Canada and Mexico.
Asked during his appearance with Trudeau whether NAFTA was dead, Trump said, "We'll see what happens".
Trade experts say the NAFTA talks are likely to stall in the face of aggressive USA attempts to sharply increase content requirements for autos and auto parts.
"We all understand that it has worked", he said of the 23-year-old North American Free Trade Agreement, before adding, "As we think about redoing trade agreements between Canada, the USA and Mexico, there is opportunity for improvement".
"If we can't make a deal, it'll be terminated and that will be fine", Trump said, using his typical bare-knuckle approach to top level diplomacy.
"If every marriage had a five-year sunset clause on it, I think our divorce rate would be a heck of a lot higher", Canada's ambassador to Washington David MacNaughton said last month.
Canada and Mexico want their companies to be able to bid on more USA federal and state government contracts, but this is at odds with Trump's "Buy American" agenda.
The two leaders met as negotiators from the U.S., Canada and Mexico were convening in a Washington suburb for the fourth round of talks on reworking the North American Free Trade Agreement.
U.S. Chamber of Commerce CEO Thomas Donohue, speaking in Mexico City on Tuesday, pledged to fight "like hell" to defend Nafta if Trump tries to pull out. Mexico could leave NAFTA and have the strength to move on without any serious long-term structural damage to the economy, he said.
Rep. Richard Neal of MA, the ranking Democrat on the committee, said he hopes NAFTA will expand Canadian market access for US cultural industries and "will be an opportunity to update intellectual property rules".
NAFTA negotiators face tough new USA demands to increase regional content for autos to 85 percent from 62.5 percent, with 50 percent from the United States, according to people briefed on the plan.
Americans", she said, and acknowledged that changes to the deal would "of course be opposed by entrenched Washington lobbyists and trade associations.
"Without a doubt, there's life after NAFTA", he said, "And that's what gives us strength in the (current) negotiations".
"There's a path to be optimistic", he said.
"U.S. negotiators have made conditions so tough that Mexico and Canada could reject them, which would be the ideal excuse for the US government to announce its departure from NAFTA", Coutino wrote.
"In terms of trade, the US sells more to Canada than it does to China, Japan and the United Kingdom combined".