WASHINGTON (Reuters) - U.S. President Barack Obama, Canadian Prime Minister Justin Trudeau and Mexican President Enrique Pena Nieto will meet in Ottawa for a North American leaders’ Summit on June 29, the White House said on Wednesday. The “Three Amigos” summit, with two key U.S. trading partners, comes as Obama grapples with a wave of anti-free-trade sentiment that has stalled ratification of the Trans-Pacific Partnership (TPP), a sweeping 12-nation pact that includes Canada and Mexico. Obama hopes the U.S. Congress will ratify the deal before he leaves office on Jan. 20. But trade has become a lightning rod issue in the presidential election campaign to replace him. Republican Donald Trump, now his party’s presumptive nominee for 2016, has attacked the TPP and describes the tripartite  North American Free Trade agreement as a disaster that needs to be renegotiated or broken. In the Democratic campaign, Senator Bernie Sanders has opposed the trade deal, and Democratic front-runner Hillary Clinton has also expressed concerns. Canada sends 75 percent of its exports to the United States and would suffer greatly if a future president moved to clamp down on free trade. Trudeau, asked how he would deal with a President Trump, said the leaders of both countries would always agree on the need for growth and prosperity. One important way to achieve this was through trade, he added. “The level of integration between the Canadian and American economies is unlike anything else ... in the world,” he told a news conference in Ottawa.    The last “Three Amigos” summit was in Toluca, Mexico in 2014. Canada was supposed to host the meeting early last year but canceled it amid tension between then Prime Minister Stephen Harper and Obama over the Keystone XL pipeline. Obama will address Canada’s Parliament during the visit, the White House said. He last came to Canada for a bilateral visit in February 2009, the first foreign trip of his presidency. Ottawa’s relations with Mexico are strained over Canadian rules, introduced under Harper, that impose visas for visiting Mexicans. Trudeau said he hoped to be able to announce within weeks that the requirement would be scrapped. 