You would not be able to reclaim your bag if you headed into the city since it goes to a carousel in the special transit area to be collected after you clear US immigration. This is a glassed off area from which you pass a customs agent who lets you join the YVR-boarding passengers at the area where the bag goes back onto the belt to the aircraft, and you go through security.

I suppose you could let your bag sit on that belt where is might be set aside for later collection. Then after you've cleared YVR-originating Immigration, ask the Customs people if you can go to the connecting area to collect your bag. It would be risky, but otherwise you will have to take your bag with you between flights since it can only be checked once you've cleared US Immigration and Customs.