The two other sources, who are involved in the trade talks and asked not to be named, said that Mexico remains firm on its position to get up and leave from the negotiating table if Trump goes through with the move.
His comments were made a day after Canada filed with the World Trade Organization (WTO) almost 200 complaints that Americans breeched global trade rules.
Ms. Freeland said Canada intends to put forward new proposals at the Montreal talks, but did not provide specifics.
Tough-talking Liberal cabinet ministers are delivering a collective message that Canada will "stay strong" to defend the country's interests in the face of escalating trade tensions with the United States.
But when Public Safety Minister Ralph Goodale went to Kentucky last week, he gave a speech in which he warned the Americans against "tanking the whole relationship".
Canadian companies and industries that would be most acutely impacted by the pact's demise are largely stuck in neutral given the uncertainty of what might replace it, analysts and executives have said. While she said Wednesday's news of Canada's WTO challenge is a separate issue from NAFTA that is primarily focused on the ongoing softwood-lumber dispute, Trade Minister François-Philippe Champagne said the challenge was aimed at sending a broad message to the U.S.
"Our approach from the start has been to hope for the best, but prepare for the worst, so Canada is prepared for every eventuality", Canadian Foreign Minister Chrystia Freeland said, according to local media.
"We believe it is absolutely possible, if there is goodwill on all sides, to have a positive outcome in Montreal", she said.
"When it comes to the more unconventional USA proposals, we have been doing some creative thinking", she said.
"We are going to Washington to show that Canadians speak with one voice when it comes to the important matter of trade with the United States", she told guest host Terry Milewski.
"There's nothing that Canada could do, short of setting fire to the White House again, that would change the trajectory of whatever it is that Donald Trump is going to do", she said in reference to an 1812 war.