Alternate route: just walk there

If you ask Google Maps to calculate directions between Detroit, Michigan and Windsor, Ontario—the only point where you go due south to enter Canada from the United States—and then ask for directions via public transportation, here’s what you get:

And here’s what you get if you reverse those directions:

There are, of course bus services operated by both cities’ transportation systems, naturally. I am uncertain as to whether you can walk through the Detroit-Windsor tunnel, though.