Originally Posted by taupo

Easy to do.
Ignore some of the above posts.

Exit the secure area from your domestic flight, meet your family, enjoy lunch.

When you come back to YVR, go to US Departures with boarding passes, passports and completed US CBP in hand, pass through duty free, then to US INS. After INS but before US Customs, make a left turn into the US Connections baggage hall, claim your bags, then proceed through US Customs where they will take the card, drop checked bags on the belt, through security, MLL and plane.

Allow an hour to do all that. US INS and security can be very fast to get through, can also extremely slow. If fast, the whole process is 10 minutes or less.