Canadian Prime Minister Justin Trudeau, shown here at a news conference last month, presented a… OTTAWA—Canadian Prime Minister Justin Trudeau on Monday unveiled a national carbon-pricing proposal that sets a minimum amount the country’s provinces would be required to adopt within two years. In a speech to the country’s parliament, Mr. Trudeau said the proposed price on carbon pollution would start at 10 Canadian dollars ($7.62) a metric ton in 2018, and rise steadily to C$50 a ton in 2022. Mr. Trudeau said Canadian provinces would have to decide how they implement the pricing plan — either through a carbon tax or a cap-and-trade system, which would need to be stringent enough to meet government’s 2030 target of reducing carbon emissions by 30% from 2005 levels. Mr. Trudeau said if a province doesn’t have a system in place by 2018, Canada would implement a pricing regime for that jurisdiction. […]