Prime Minister Justin Trudeau is heading to Mexico and the United States next month, at a time when NAFTA talks are growing more contentious.

Trudeau will be meeting with Mexican President Enrique Pena Nieto during a stop in Mexico, as well as U.S. officials in Washington, D.C.

Sources speaking to CBC News on background did not say if the trip involves a visit to the White House, or whether Trudeau will meet with U.S. President Donald Trump.

Trudeau has made several visits to the U.S. this year that did not include meetings with Trump.

But a government source said that although trade is always top of mind for Trudeau, it will not be the sole focus of his trip.

A second government source said the Mexico leg of the trip has been in the works for months, and is part of an overall bilateral agreement between countries.

That source said it is Trudeau's turn to visit Mexico, since Pena Nieto came to Ottawa in July 2016.

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Trudeau and Mexico's President Enrique Pena Nieto walk in the Hall of Honour on Parliament Hill in Ottawa last June. (Chris Wattie/Reuters)

At that time, Mexican visa restrictions were the most pressing issue of the day. Priorities for both countries have changed significantly, due to the outcome of the U.S.election.

Canada and Mexico have put considerable effort into defending NAFTA, and the issue is expected to come up during Trudeau's visit, even if it isn't the primary focus of discussions.

Fewer details are available about the Washington portion of the trip, as specifics are still being finalized.

Talks grow heated, ambassador says

The third round of NAFTA talks is set to wrap up in Ottawa on Wednesday.

Canada's ambassador to the U.S. said discussions are unfolding "pretty much as we expected," but at times talks have been "a little more than heated."

David MacNaughton shared the update with a luncheon crowd at the Canadian Club of Toronto on Tuesday.

Round 3: NAFTA negotiations7:51

"We are making progress, but it is hard work, and there is a lot more hard work ahead," MacNaughton added.

Multiple sources have told CBC News that the U.S. has been slow to present specific details of changes it would like to see in NAFTA.

U.S. negotiators have not presented proposals on some of the most contentious issues, including rules of origin, how dispute will be resolved, or the dairy industry.

Canada's Foreign Affairs Minister Chrystia Freeland will provide an update on the progress of talks alongside her Mexican and U.S. counterparts on Wednesday.