I am a US citizen traveling SFO-YVR-PEK and my return is PVG-YVR-SFO. On the return leg, do I have to clear customs in YVR and SFO, or just SFO, or just YVR? All flights are on Air Canada / Rouge, Terminal M - Main.

Also, my return layover is only 90 minutes in YVR, do you think that is long enough?

Thanks