Remember that "hydro" is a synonym for electricity in many parts of Canada.
As you go north there are a lot of rivers in Canada (not to mention Niagara). This has been heavily utilized in Quebec (significant portions of which are exported to the US), as well as Ontario and BC, with smaller amounts elsewhere. While Canada has lots of oil and coal production, it is limited to a couple regions and not the ones with the greatest electricity use (though in places like Alberta these are used much more heavily).