I use ForeFlight with subscriptions to both U.S. and Canadian charts. Users are required to toggle between one and the other - they don’t display simultaneously. The Canadian charts (provided by Nav Canada) extend between 50 and 60 nm into the U.S. in Western Canada (from the Prairies/Central Plains to the West Coast). It’s complicated around the Great Lakes, but in Maine the Canadian coverage is as much as 100 nm south of the border.