It would be completely idiotic to cut the goaltender who performs best at camp, just because he's a year younger than the rest. It's not like Cann hasn't been under this type of pressure before, after leading Canada to the Under 18 gold last year.
I could see that sort of train of thought working if you've got 3 goaltenders who have all performed at the same level, and you want to give the spot to the older guys who are on their last chance to play for team Canada.
But you pick the best players out there, regardless of age. If Cann is clearly the best goalie at camp, you take him. If John Tavares is one of the best forwards at camp, you take him. Whatever players are going to give your squad the best chance of bringing home the gold, you select them. Age should not be a factor if said player is clearly the best.