Not sure about this "transfer" process. When I did SAN-YVR-YYC a few weeks ago, there was a YVR employee in the customs area asking people if they had connections in order to help them out with the "express" service, but when I asked him, he said it was only for checked bags. As we had only carry-on bags, we were directed to go through customs and then over to domestic security etc as normal.

On the bright side, it seems that while there's no longer anyone manning the NEXUS/priority security at domestic, if you have NEXUS, they'll let you through the little NEXUS lane off to the side pretty much any time - much more civilized than when they seemed to shut it down at 7:30 or 8PM or something like that.