And even as Trump, Trudeau and Peña Nieto - on his final day in office -signed the accord on the sidelines of the summit, officials from the three countries continued to haggle over terms for lifting United States tariffs, according to The Washington Post.
Canada will also provide new access for US chicken and egg exports, and increase access for turkey.
The new trade deal, which will govern more than a trillion dollars of trade, came after more than a year of acrimonious negotiations.
The Prime Minister's Office confirmed the signing late Thursday after a day of some uncertainty, with Foreign Affairs Minister Chrystia Freeland saying there were still details to be finalized before the three countries could formally sign the "massive" deal.
The deal still needs to be ratified by all three countries' lawmakers. "We've taken a lot of barbs and a little abuse and we got there", Trump said of the pact.
A Canadian official also said earlier Friday that the big advantage of signing onto the agreement now is a side letter on the auto industry exempting Canada of potential tariffs on exports of up to 2.6 million vehicles - well above current levels.
This may prove most challenging for Mr Trump, as the Democrats take control of the House of Representatives from January.
Tariff tensions shadow US, Canada, Mexico trade pact signing
'Our objective has always been to sign this agreement on November 30 and we are on track to hit that objective, ' Freeland said shortly after the Canadian delegation arrived in Argentina, according to the Canadian Press.
Mr Trump forced Canada and Mexico to renegotiate the 24-year-old agreement because he said the existing pact encouraged USA companies to move jobs to low-wage Mexico.
Turning to address Trump, said "And Donald, it's all the more reason why we need to keep working to remove the tariffs on steel and aluminum between our countries".
The signing came at the front end of two days of tough diplomacy for Trump.
There is no formal meeting between Trump and Trudeau on either leader's schedule for the Friday and Saturday summit. Posing for photos in the gilded Salón Blanco, Trump spoke about their longtime personal relationship and said they would discuss trade, military purchases and other issues. The businessman-turned-politician joked that when he and Macri first met they'd never have imagined their future roles on the world stage. He is trying to halt economic turmoil that has caused the steep depreciation of the Argentine peso. His agenda for the weekend includes meetings with world leaders, as well as a number of heavily choreographed group activities for the gathering of leaders of rich and developing nations.
Mr Trump tweeted he was axing the meeting with Russia's leader shortly after his former lawyer Michael Cohen admitted lying to Congress about a Trump property deal in Russian Federation. Trump has denied any wrongdoing.
This second requirement was put in place to prevent auto manufacturers from favoring Mexico, which allows companies to pay workers lower wages, over the United States.
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