Originally Posted by
schnitzer
Does anyone know if I am required to clear US Customs on this trip from Narita to Vancouver via San Francisco?
NRT > SFO - UA838
SFO > YVR UA1116
You will need to clear U.S. Customs at SFO, and then Canadian Customs at YVR. There will be no recognition in Canada of where you started your journey, the bottom line is that you arrived into Canada from the U.S.
One small note: On the Canada Customs form, you will need to check the "Other Country via U.S." box when answering where you came from.
Side note: It looks like you have about one hour and 45 minutes in connection time at SFO. Don't delay when leaving U.S. Customs and going to your connecting gate.