Prime Minister Justin Trudeau says he's not worried the election of Republican front-runner Donald Trump or Democratic contender Bernie Sanders could lead to the dismantling of the North American free-trade agreement.

Mr. Trump has called NAFTA a "disaster" and vowed to either "renegotiate it or we will break it" if he's elected president. Mr. Sanders has also described the trade pact as "disastrous" and attacked Democratic front-runner Hillary Clinton for supporting the deal.

The influential U.S. Chamber of Commerce, which invited Mr. Trudeau to speak at a breakfast gathering in Washington, is concerned about the heated protectionist rhetoric against NAFTA. Chamber vice-president Myron Brilliant told Mr. Trudeau the trade pact has "done more good to prosper our two nations and Mexico."

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The Prime Minister also spoke glowingly about NAFTA and called for an "increasingly integrated North America," but he was less pessimistic about the dangers to the trade deal, suggesting the political posturing is simply part of the election cycle.

"We have to understand that trade is ultimately good, not just for our countries but for business and our workers," Mr. Trudeau later told CNBC. "I'm not worried that we are going to reopen NAFTA or other trade deals. The challenge is once you open it a little bit, they all tend to unravel and it's too important for our economies to continue to have a strong trade relationship."

The Prime Minister is in Washington to attend the Nuclear Safety Summit – his second visit to the U.S. capital since he was feted by President Barack Obama at a gala state dinner on March 10. He held bilateral meetings with the leader of Argentina and will attend a summit dinner hosted by Mr. Obama at the White House.

Mr. Trudeau was also pressed by the U.S. Chamber of Commerce to move quickly to ratify the 12-nation Trans-Pacific Partnership before the end of the year. The massive trade deal is opposed by Ms. Clinton as well as by Mr. Trump and Mr. Sanders.

"This is the opportunity for Canada and the United States to show leadership," Mr. Brilliant said. "It is so important strategically for the United States and for Canada and the other countries that we move forward."

The Prime Minister, who promised during the election to hold public consultations on TPP, gave his strongest indication that Canada will ratify it if President Obama can get the U.S. Congress to approve the deal.

"In our conversations with Canadians, with industries which are ongoing, there are a lot of people in favour of it and there are a few who have real concerns and we're looking at understanding and allaying certain fears and building on some of the opportunities," he said.

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The breakfast event included representatives from several major U.S. corporations, including General Electric, Ford Motor, Google, Amazon, Oracle, Coca-Cola and John Deere, as well as the World Bank.

Mr. Trudeau used the breakfast to tout last week's federal budget and held out the prospect of the investment opportunities for U.S. business on the billions of dollars of infrastructure projects announced in the budget.

"Over the course of the next year, we will work to develop a long-term infrastructure strategy that includes large-scale infrastructure projects and investments in our ports and important trade corridors to the U.S. and Asia," he said.

Mr. Trudeau sounded a positive note about Canada's economic prospects despite the plunge in oil prices that has left thousands of people unemployed and pushed the Canadian dollar to a 13-year low.

"Canada, quite frankly, with its diversity, with its geographical strength, with its human resources and natural resources, we're well positioned to grow in the coming years," he said.

Mr. Trudeau was asked about resurrecting the cancelled Keystone XL pipeline but said "it's not a government of Canada proposal," though he acknowledged the need to get "our resources to market." He blamed former Conservative prime minister Stephen Harper for Keystone's rejection by the Obama administration because he failed to act seriously to combat climate change.

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Later, Mr. Trudeau attended a luncheon put on by Japanese Prime Minister Shinzo Abe, who will be hosting the G-7 summit in Japan in May. The Japanse leader said his biggest concern was the slowdown in the global economy.

"As the prospects of the global economy have become increasingly unclear, due to concerns about the slowdown of the Chinese economy and other causes, many prominent economists and experts are now predicting a further deterioration of the economic situation this year," he said.

Mr. Abe and Mr. Trudeau have both advocated for stimulus spending to kickstart growth. "Japan and Canada are aligned in focusing in investment as opposed to austerity," Mr. Trudeau said.

Mr. Abe had met in the morning with President Obama and South Korean President Park Geun-hye to present a united front over recent nuclear and missile tests by North Korea.

Relations between Ms. Park and Mr. Abe have been frosty in the past, but the two have been brought together in recent months by shared concerns about North Korea, which conducted a fourth nuclear bomb test on Jan. 6 and launched a long-range rocket into space last month.