Trump made the comments late Wednesday as part of a free-wheeling news conference at the end of the United Nations General Assembly.
Relations between the two neighbors have been strained since Trump assailed Trudeau at the G-7 meeting in June, calling him a "weak" and "dishonest" back-stabber.
Trump had kind words for incoming left-wing President Andres Manuel Lopez Obrador, calling him "great".
After spending the last few days meeting with other world leaders, speaking about Canada's contributions globally, and campaigning for a seat on the UN Security Council, the ongoing uncertainty over NAFTA and tensions between Trudeau and U.S. President Donald Trump persisted.
But the president wasn't done.
Trudeau said the deal between the US and Mexico raises the "possibility" of Canada signing on, but that he's standing up for Canadian interests in negotiations.
"Yeah I did", Trump said. "That's the big one".
"If we push it beyond that date, then we have a new negotiation with Lopez Obrador and we don't know where that would go at all", Lighthizer said.
He added that he and his team does not like Canada's "representative".
Canadian officials said they do not believe Trump can rework NAFTA into a bilateral deal without the approval of Congress.More news: PM Netanyahu Meets with US President Donald Trump in NY
Trump is threatening to impose tariffs on Canadian autos.
"It could take a little more time".
"We will keep working as long as it takes to get to the right deal for Canada", Trudeau earlier told reporters at the United Nations.
"There are things where, basically, we're just not prepared to give in because it would really render the agreement meaningless", MacNaughton said in a public interview with Politico in Toronto.
The pressure, of course, is mounting.
As the NAFTA negotiations are wrapping up, and after a successful renegotiation of the US-South Korea free-trade agreement, the Trump administration's focus appears to be shifting to trade talks with Japan.
A Trump administration official has stated the side deal reached between the USA and Mexico is set to be published on Friday. I've never liked it, it's been very bad for the United States. 232 of USA trade law.
According to the Agency, the canadian party declared that "no meeting has not been requested". Freeland's office did not respond to a request for comment. Trump stayed seated, as they had a brief exchange and shook hands, but later stood up for interactions with th e leaders of Mexico and Egypt.
Lopez Obrador responded he would be "open to the possibility" in the absence of a trilateral agreement that also included Canada, said Hector Vasconcelos, a foreign policy advisor to Lopez Obrador's campaign who listened to the call on July 2.