To answer the OP's question, yes, you will have to deplane in YVR and go through Canadian immigration/customs, then back up to US preclearance and through security to get through to the US departure gates. Very unlikely you'd make it back on the same aircraft unless you have over one hour on the ground. I believe flight crew is exempt from customs if they're doing a quick turnaround, but passengers do not have the same luxury.

Travellers seem to have more negative experiences getting through CBSA at YVR than at other airports. I am a US citizen with no status in Canada other than frequent visitor, and I've never had a problem with CBSA. My last interaction with them at YUL took about 10 seconds; the only question the officer asked is "how long are you staying?" before telling me to enjoy my stay and sending me on my way. Even when I got sent to secondary once before, the officers were as nice as could be. US CBP has always been much more intrusive and rude-mannered with their questioning in my experience.