Call Air Canada with date, flight number and last name they will assign a seat and give you Record locator for future travel. There is a website links all over advising what the transfer process via YVR and whether it is so able or not. I think if on the same ticket and they are aware of inbound connection they will monitor your status via both carriers as neither one wants you stranded in Canada. I also anticipate like EWR UA pads their schedule extensively so even 65 minute in queue for takeoff and you still land on time.