Donald Trump needs to butt out as a hovering presence over the North American Free Trade Agreement talks and U.S. lawmakers must come clean about what they really think of the deal, says a veteran Liberal MP.

Bob Nault, who heads the House of Commons foreign affairs committee, will be taking his blunt assessment directly to Capitol Hill in the coming days.

Nault leads an all-party delegation of Canadian parliamentarians south of the border this week for meetings with their legislative counterparts — first to Mexico City and later in the week, Washington.

The visit comes amid the full court press already being mounted by the Trudeau government, which includes sending cabinet ministers to key U.S. states, and pushing the premiers to reach out to their top customers and American state counterparts to save NAFTA.

The recently-ended fourth round of NAFTA has stoked major fears the 23-year-old trade deal could end with a U.S. withdrawal because American negotiators tabled potentially deal-killing proposals on dairy, autos and other issues that Ottawa views as non-starters.

'Let the negotiators do their job'

Nault says the time has come to start asking members of the U.S. Congress a very basic question.

"I'm going to Mexico and the United States to get one question answered that's on everyone's mind: do people want a NAFTA deal or not?" he said in an interview.

"The role that Congress plays is very, very important and if the government of the United States and its representatives is not interested in the deal they should probably tell us and not put forward pieces of work that they know we would never agree to at the negotiating table."

Nault also took aim at Trump directly for his anti-trade, tear-up-NAFTA-rhetoric, which is an area where Prime Minister Justin Trudeau and Foreign Affairs Minister Chrystia Freeland have navigated carefully.

"The last time I looked, the U.S. is not a dictatorship, and neither is Canada or Mexico. So this isn't about one individual, whether it is the president of the United States or the prime minister of Canada."

Liberal MP Bob Nault says he thinks "Canadians are a little too polite for their own good." (Supplied)

Nault said the virtual presence that Trump has at the negotiating tables — through social media even though he's not physically in the room — is an unprecedented phenomenon, at least in the three decades the Ontario Liberal MP has been in politics.

And, he added, that's just not helpful.

"My recommendation to him and his administration is to let the negotiators do their job, and do it quickly with a very firm understanding of what the direction is," said Nault.

"I don't see any rationale for suggesting it's a bad deal — they're going to rip it up, they're going to give notice and those kinds of tactics. I don't think it really works for anybody."

The gap that has emerged between the U.S. positions and those of Mexico and Canada has now raised the stakes for elected politicians in all three countries, he said.

Canadians can be too polite, says Nault

Nault said the time has come for lawmakers in all three countries to "play their role signalling to their governments that they support or don't support NAFTA or renewed NAFTA."

Nault's tough talk is not part of a good-cop, bad-cop strategy by the Trudeau government. As the head of a parliamentary committee, Nault said he and his fellow Conservative and New Democrat members enjoy a degree of autonomy to speak on behalf of the people they were elected to represent.

He also dismissed any suggestion that a harder-edged approach in the U.S. could do more harm than good.

"I think Canadians are a little too polite for their own good. And when you're talking about a business deal, it's not about your charm or your politeness," said Nault.

"I think we're sending that message through Chrystia Freeland. But I think it wouldn't hurt to send it more."

Freeland spoke directly to Americans herself on Sunday, appearing on a CNN talk show, where she was asked whether she thought the U.S. was trying to sabotage NAFTA.

"Canada is kind of like the girl next door. It's easy to take us for granted," she said.

Freeland recalled what Pepsi CEO Indra Nooyi once told her during an interview.

"Always assume positive intent from your counter-party. You don't always have positive intent. But you should assume it," she said.

"If one party has a winner-take-all attitude then it's not going to work."