I actually checked it out with Elections Canada. It's up to the returning officer in each riding to determine the polling locations in that riding, and it's done on a negotiated basis.
I can tell you anecdotally that any regularly scheduled activity is often pre-empted by a polling station, whether churches, aerobics, or scouting. Whatever the regularly scheduled activity, it's often pre-empted for the polling station. I'm telling you that anecdotally because I've heard numerous instances of that happening. I don't have statistics for it, but it seems to be a common enough experience that other activities are set aside for election day.