My experience on these flights have always been:

JFK-YVR-HKG: Required to stay on board aircraft in YVR

HKG-YVR-JFK: Required to get off aircraft in YVR and wait in glassed off gate area. Contrary to the previous poster, I found the gate area very nice. It has always been clean, and has complimentary bottles of water and juice, bathrooms, and plenty of seating. Once, during a delay, they even brought in sandwiches and snacks during the wait.