http://www.cic.gc.ca/english/helpcentre/answer.asp?q=188&t=17
I have applied for a new work permit. Can I stay in Canada if my work permit expires?
Yes. You can stay in Canada, and may be able to keep working, under what's called implied status. That means the law implies you are a temporary resident. The implied status lasts until Citizenship and Immigration Canada (CIC) decides on your new permit application. However, you must respect the following requirements:
If you applied for another work permit
•You must stay in Canada and meet the conditions of your original work permit. If you applied for a work permit extension before your work permit expired, you can keep working under the same conditions as your existing permit until CIC decides on your application unless you have applied to extend your stay under another category.
If you applied for a different kind of permit
•You cannot do any of the activities allowed by the original work permit. For example, you may have come to Canada as a worker and then applied for a study permit. If so, you must stop working once your work permit expires. After that, you cannot work or study until you get a new permit.