These are the requirements:
To obtain a work permit after your graduation, you must meet the following requirements:
You must have studied full time in Canada and you must have completed a program of study that lasted at least eight months.
In addition, you must have graduated from:
a public post-secondary institution, such as a college, trade/technical school, university or CEGEP (in Quebec), or a private post-secondary institution that operates under the same rules and regulations as public institutions (currently only qualifying programs of 900 hours or longer leading to the Diplôme d'études collégiales (DEC) or Attestation d'études collégiales (AEC) at private college-level educational institutions in Quebec are eligible), or
Canadian private institution authorized by provincial statute to confer degrees but only if you are enrolled in one of the programs of study leading to a degree as authorized by the province and not in all programs of study offered by the private institution.
You must apply for a work permit within 90 days of receiving written confirmation (for example, a transcript or an official letter) from your institution indicating that you have met the requirements for completing your academic program.
You must have completed and passed the program of study and received a notification that you are eligible to obtain your degree, diploma or certificate.
You must have a valid study permit when you apply for the work permit
This is on the CIC website at http://www.cic.gc.ca/english/study/work-postgrad-who.asp
Also, if you have an off-campus work permit, you can continue working on it after you graduate until you get your post-grad permit.