I'm not 100% certain what the question is, but if you arrive at YVR from the US on Air Canada or WestJet, you can connect to a domestic destination without going through customs or claiming your bag. Keep eyes peeled for staff handing out cards to identify you as an ITD (Intl -->Domestic) passenger. As you descend the escalator/stairs into the main immigration hall, make a hard right and clear CBSA immigration at a kiosk* in a separate ITD area (almost underneath those same stairs). From there, you'll be herded into a glass corridor and onto a bus waiting outside that will drive you to Gate 29 (post-security) in the C pier, from which you can stroll to your domestic departure gate. No additional personal screening required. Bags will be sent to your domestic plane and waiting for you at your destination.

*the ITD-specific kiosk area doesn't have dedicated Nexus kiosks - only the regular PIKs used by everybody. But passenger volumes should be low enough that you wouldn't gain any wait-time benefit from a dedicated Nexus line anyway.