Canada's top diplomat says she's cautiously optimistic about U.S. intentions for the North American Free Trade Agreement after hearing Vice-President Mike Pence call modernization a "win-win-win" situation.

But just days before the U.S. is expected to release its trading objectives, Foreign Affairs Minister Chrystia Freeland still won't say whether she thinks President Donald Trump is after renovations or a complete demolition of NAFTA, which first came into force in 1994.

In a speech on Friday in front of dozens of state governors, as well as Prime Minister Justin Trudeau and Freeland, Pence promised a collaborative approach.

"We will modernize NAFTA for the 21st century so that it is a win-win-win for all of our trading partners in North America," Pence said. "We're looking forward to bringing NAFTA into the future in a way that will equally benefit both our countries."

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According to Freeland, Pence "underscored that in his bilateral meeting with us and said that was a very intentional remark. I think that's a great attitude for the United States to have going into these negotiations."

Trade talks can bring 'twists and turns'

Freeland, a former journalist, was taking notes during Pence's speech and said she drew three stars beside his win-win-win comment.

"That kind of approach is really rational based on the objective reality of the relationship, so I am cautiously optimistic," she said in an interview with Catherine Cullen on CBC Radio's The House.

"But, you know, trade negotiations — as we know with [the Comprehensive Economic and Trade Agreement] — even between the best of friends who have shared objectives, trade negotiations can have lots of twists and turns."

On Monday, 30 days before formal talks begin, United States Trade Representative Robert Lighthizer's office is expected to publish his negotiating objectives, outlining the Trump administration's path going forward.

"I have some ideas of what I am looking for, and I have some ideas about what I'll take as a good sign and as a less good sign, but I'm not going to prejudge it until I've seen it," said Freeland.