It may be answered here.
http://www.cic.gc.ca/english/information/applications/guides/5551E2.asp
May I leave, then re-enter Canada?
In order to return to Canada, you must be in possession of a valid passport or travel document.
You also need to hold a valid study or work permit if you are returning to study or work in Canada.
If you are a citizen of a country that requires a temporary resident visa (TRV) to travel to Canada, you will also need to be in possession of a valid entry visa to return, unless:
you are returning to Canada following a visit only to the United States or St-Pierre and Miquelon; and
you return before the expiry of the period initially authorized for your entry or any extension to it, either as a visitor, student or worker.
Possession of these documents does not guarantee re-entry. All persons must establish that they meet all of the requirements of The Immigration and Refugee Protection Act and Regulations before being authorized to enter or re-enter Canada.
Note: Citizens of the U.S. do not require passports or travel documents to enter or return to Canada. Permanent residents of the U.S. do not require passports or travel documents if they are entering or returning to Canada from the U.S. or St. Pierre and Miquelon. However, both must provide documentary proof of citizenship or permanent residence such as a national identity card or an alien registration card.
