Request your school to give you Letter of Enrollment or Letter or Registration stating that you are Full-Time Registered/Enrolled student. After getting this letter you need to apply for "Confirmation to Work Off-Campus" letter from CIC. You will make that request online by submitting "Case Specific Enquiry" from this link: https://dmp-portal.cic.gc.ca/enquiries-renseignements/canada-case-cas-eng.aspx?_ga=1.144760116.1079316027.1379171408
Select "International Student – Confirmation letter to work off campus" as TYPE of form, fill the required information, attach scanned copies of your Study Permit, Letter of Acceptance and Enrollment/Registration Letter (the one which is stated in above paragraph) and submit the form. You will get this "Confirmation to Work Off-Campus" letter within 10-12 working-days via email.
Thanks for the clear explanation on this issue. What if it is stated clearly on the study permit that, the holder of
Now bring that "Confirmation to Work Off-Campus" letter which you will receiver via email from CIC, your passport and study permit paper to Service Canada Center and you will get your SIN.
All the best.