If you have a valid study permit, work permit, or visitor record, and you leave Canada and visit only the United States, you do not need a valid temporary resident visa (TRV) to re-enter Canada. (See the Immigration and Refugee Protection Regulations, Part 9, Division 5, Section 190:3f). This also applies to visitors, provided you return to Canada by the end of the initial period authorized for your stay in Canada (typically six months or less).
YOU DO NOT NEED A TRV TO FLAGPOLE AS LONG AS YOU HAVE A VALID PERMIT!