As a graduate student in Canada you are allowed to work for up to twenty (20) hours per week. For many students, these hours will be taken up by a Graduate Teaching Assistanceship (GTA) through your department. Contact your supervisor or departmental graduate secretary for information on GTAs.
As of June 1, 2014, study permits will automatically authorize the holder to work off-campus for up to 20 hours per week during the academic session and full-time during scheduled breaks without the need to apply for a separate work permit. The study permit holder must be pursuing academic, vocational or professional training of six months or more that leads to a degree, diploma or certificate at a designated institution.
More information about the new regulations of international students can be found through Citizenship and Immigration Canada.