I know people always give us XJT guys grief for it (as if it's OUR choice) but I am doing IAH-YYZ tommorow. Seems like that should be a mainline route just based on the distance and the fact that its the 4th largest US city and largest Canadian city. But Air Canada flies the route (and YUL-IAH, YYC-IAH) with Jazz CRJ-700s and the occasional E170 so there must not be as much demand there as you'd think.