Trade talks between the United States and Canada resumed Wednesday morning as the two nations scrambled to reach a deal by the end of the week that would keep the three-country North American Free Trade Agreement intact.

The United States and Mexico earlier this week agreed to a bilateral trade pact and said Canada had just days to sign on to the agreement or be excluded.

But pressure is growing on President Donald Trump to include Canada in any pact, with lawmakers increasingly suggesting that a bilateral agreement will not pass congressional muster.

On Wednesday, Chrystia Freeland, Canada’s foreign minister, expressed optimism that the talks were going to move in a positive direction this week.

“Mexico has made some significant concessions which will be really good for Canadian workers,” Freeland told reporters outside the office of the U.S. trade representative. “On that basis, we are optimistic about having some really good productive conversations this week.”

Freeland held a brief meeting with Robert Lighthizer, the U.S. trade representative, on Tuesday evening after rushing to Washington from Europe. Following that meeting, she met with Mexican officials to discuss the trade agreement they reached with the United States.

The Trump administration may be more willing to strike a deal with Canada given the blowback from Congress. The potential for a NAFTA that includes just Mexico could result in a showdown with Congress, which has the ultimate legal authority over trade agreements.

White House officials have been attempting to sell the agreement it reached with Mexico as one that Canada cannot refuse, but several issues still remain to be worked out between the United States and its Northern neighbor — including Canada’s dairy tariffs and a legal framework for settling trade disputes.

Legal experts remain divided about what would happen to the U.S.-Canada trading relationship if they are no longer knit together through NAFTA. Relations between Canada and Mexico would likely be governed by the Trans-Pacific Partnership, which the countries are likely to approve early next year.

But that pact excludes the United States and the relationship could wind up reverting to the rules of an earlier U.S.-Canada free trade agreement.

Also unclear is whether the United States can move forward with a bilateral deal with Mexico without terminating NAFTA and restarting the process of notifying Congress about the administration’s intentions.