Prime Minister Justin Trudeau told an economic summit on Friday that he believes U.S. President Donald Trump is sincere in his desire to annex Canada and that this stems from the American leader’s interest in gaining access to this country’s critical minerals, a source said.

Mr. Trudeau made the comments to an audience of about 200 business leaders, trade experts and union executives in Toronto who have gathered to map out ways to boost economic growth and attract new capital investment in the face of the looming threat of U.S. protectionism.

Mr. Trump has repeatedly proposed to Canada in recent months that it could avoid tariffs if it agreed to a political union with the United States. He has mockingly referred to Mr. Trudeau as the governor of the 51st state.