Originally Posted by Nayef

Are you flying to the US via Vancouver from another place in Canada or from a third country? Because if you're taking a domestic flight to Canada then board a US-bound flight, you won't need to re-check your bag in Vancouver (as long as it's all the same ticket). I think your checked luggage will go directly to your US destination whenever you do unless it's separate tickets. (That's as far as my experience flying from Toronto to the US: you don't bring your checked bags through US preclearance.) Your best bet is to call the airline and ask what happens to your bag during your layover if the two flights are on the same ticket.