Calling for a "thinner border for trade, not a thicker one," Canadian Prime Minister Justin Trudeau on Friday told United States governors that he would oppose any Trump administration efforts to reform the North American Free Trade Agreement (NAFTA) in a way that would inhibit trade between member countries.

"More trade barriers, more local-content provisions, more preferential access for homegrown buyers and government procurement, for example, does not help working families over the long-term or even the middle-term," Trudeau said at the National Governors Association's annual summer meeting in Providence, R.I. "Such policies kill growth."

President Trump has repeatedly criticized and vowed to renegotiate the free trade agreement. Trudeau agreed that "NAFTA isn't perfect" and said he welcomes efforts to update it, but he cautioned that "we must get this right. Sometimes getting it right means refusing to take the politically tempting shortcuts."

Trudeau was the first leader of a national government to address a meeting of the National Governors Association in its 109-year history. His presence, along with numerous other Canadian federal and provincial officials, Mexican representatives, and officials from Vietnam, China and Japan, signaled a marked international shift for the governors. As Trump has pulled back on trade agreements and promised to pursue an "America First" strategy on international relations, many governors -- Democrats and Republicans -- have stepped up their efforts to appeal to foreign leaders themselves.

"With all the inconsistencies and conflicting information coming out of the White House messaging on trade, our message to foreign leaders is: Do business directly with the governors," said Virginia Gov. Terry McAuliffe, the outgoing chair of the governors association. "What's coming out of the White House is scaring other countries. It's stifling our ability to create economic activity."

Vice President Mike Pence also spoke to the governors on Friday. While the bulk of his address was focused on Obamacare repeal efforts, he said the White House "in the coming weeks" will "modernize NAFTA for the 21st century so it is a win-win-win for all of our trade partners across North America."

For his part, Trudeau seemed to welcome the opportunity to work more directly with governors, vowing in his address "to step up our engagement across all different levels" of government in the United States. Governors, he said, "are better connected than some folks in Washington to realities of people in their day-to-day lives." He added that state leaders are better equipped to show the "tangible benefits of trade, the benefits of a global perspective."

Trudeau's sentiment was echoed at the meeting by Ontario Premier Kathleen Wynne, who advocated for "strong subnational relationships" between states and provinces, and directly between municipalities in the U.S. and Canada.

"If we see this relationship in North America as a zero-sum game, then it will be competitive, then it will be that race to the bottom," she said. "It will degenerate into a trade war."

Mexico City Mayor Miguel Ángel Mancera, who also heads the association of Mexico's governors, made a similar plea for maintaining free trade throughout North America.

"We are stronger," he said, "if we remain together."

*CORRECTION: This story has been updated to reflect the fact that while Justin Trudeau is the leader of the Canadian government, he is not the "head of state." Queen Elizabeth II is.