In that case, the election officer would have the elector vote, and the ballot that is cast would be recuperated by Canada Post, remitted to the office of the returning officer and then sent to Ottawa where it would be counted in the appropriate riding. The riding where a person is from would be determined at the time, on campus, when applying to vote by special ballot. In those places, you have people who can vote for the riding and other people who actually come from another electoral district.
On June 17th, 2021. See this statement in context.