0644 GMT July 21 2017
In the past, Donald Trump had described the pact between the US, Mexico and Canada as "the worst trade deal ever" made for Americans and vowed to rip it up or have it changed to the advantage of the US nation.
Trudeau's defense of the 1994 trilateral North American trade agreement comes ahead of the NAFTA renegotiation scheduled for August.
"More trade barriers .. does not help working families over the long term, or even the mid-term. Such policies kill growth," Trudeau, who is a defender of the two countries' trading relationship, told a meeting of US National Governors Association in Providence, Rhode Island, in an oblique reference to Trump's "America First" slogan claiming to return jobs outsourced to other countries.
"And that hurts the very workers these measures are nominally intended to protect. Once we travel down that road, it can quickly become a cycle of tit-for-tat, a race to the bottom, where all sides lose," Trudeau said.
"If anything, we would like a thinner border, not a thicker one," he pointed out.
He warned that the protectionist policies Trump advocates run the risk of becoming "a cycle of tit-for-tat, a race to the bottom, where all sides lose."
"Sometimes getting it right means refusing to take the politically tempting shortcuts," Trudeau said.
Trump's fierce opposition to NAFTA has prompted Trudeau's government to reach out to US leaders, including one-on-one meetings on Friday with Vice President Mike Pence and the governors of Kentucky, Wisconsin, Rhode Island and Iowa.
Pence, who also spoke to the Governors Association, said, "We will modernize NAFTA for the 21st century so it is a win-win-win for all our trade partners in North America."
"We are looking forward to bringing NAFTA into the future in a way that will equally benefit both our countries." he added.