I hadn't tested it before, but yes, it looks like there's coverage for some major Canadian cities near the border, including Montreal, Ottawa, Toronto, and Vancouver. You can check your locations of interest on this map[0] (requires JS). Just click "Maximum Radar Ranges" on the left and see if you fall within the coverage circles.
As I write this, there's some light precipitation just north of Toronto, and threecast seems to give reasonable output there. Note that the radar coverage areas aren't always perfect circles because terrain can block the radar beam.
Canada may have a similar system with better coverage, but I'm not sure.
