Do not let your study permit expire. Your study permit, along with your passport, is the most important immigration documents that you have. International students studying in Canada for longer than a six month period must have a valid study permit. Depending on your country of origin, most study permits will be issued for the duration of your program of study. In any case, be sure to renew your study permit at least 30 days before your current permit expires. Remember that allowing a study permit to expire is considered a violation of the Immigration Act. This means that you may not be eligible for an extension. You may also be subject to an inquiry, which could lead to deportation from Canada.
There are two types of work permits to consider, one that allows you to work off campus while taking classes and another that allows you to work or live in Canada after graduation. Follow the resource links to learn more about requirements and the steps for applying for a work permit.