I can't quote chapter and verse, but I believe that Canada is an exception to the normal rules on whatever of the seven freedoms this is. UA has shown YYZ-ORD-YVR connections in its timetables (and YYZ-ORD-SEA-YVR, before they flew nonstop ORD-YVR) since I started flying them 42 years ago. AA used to have through flights ORD-YYZ-LGA, as well (also about 40 years back).