AC does YVR-PVG 4x/week and CA, CZ, MU also have a combined total of 4, so even more restrictive than the US. Connecting in Canada isn't really better (more US cities to choose from, but the limited schedules bite) than connecting in Japan, Korea, or Taiwan, which are all much cheaper. The US3 certainly don't encourage connecting in Asia to partner flights (e.g. DL pushes ATL-SEA-PVG even though ATL-ICN-PVG is half the price).