Bell Centre is a huge arena with capacity for hockey 21,273.
Never been there though but from information online I've noticed that it has a very low capacity during concerts.
Rihanna concert at Bell Centre only 10.778 tickets available but her concert at Staples Center in LA had 19,992 tickets available and Staples is a smaller arena. These were end stage concerts and the stage size was same in both venues.
Rihanna is not the only example. A common size arena stage altough they varies a bit in size should not reduce the capacity so drastic as it does in Bell Centre.