Under the plan, all Canadian provinces must have an initial minimum carbon price — set by either a tax on fossil fuels or a cap-and-trade system — of 10 Canadian dollars per metric ton, or about $7.60. Over the next five years, the price would rise to 50 Canadian dollars per metric ton, or about $38. Mr. Trudeau acknowledged on Friday that the price set by the plan would not be sufficient to meet Canada’s commitments under the Paris climate accord.

As expected, the conservative government in Saskatchewan balked at signing the agreement. Brad Wall, its premier, said that while his province planned to significantly reduce emissions, a carbon price would make its farms, mines and oil industry uncompetitive. On Friday he said that was now particularly true if the incoming administration of Donald J. Trump pulled the United States out of its carbon reduction commitments.

“Let’s not be naïve,” Mr. Wall said.

Mr. Trudeau dismissed concerns about Canada being at an economic disadvantage relative to the United States.

“Canadian climate policies will be set by Canadians, not by whoever happens to be president of the United States,” he said.

Vice President Joseph R. Biden Jr., who was in Ottawa on Friday, tried to assuage concerns about Mr. Trump’s approach to climate issues when he addressed the leaders.