Although the international student visa for Canada does not have a provision similar to the OPT in America, the law in Canada does allow an international student to obtain a work permit for temporary employment, upon graduation, for up to 1 year in a study-related job. The student has up to 90 days after graduation to apply for and obtain the work permit from the Citizenship and Immigration Canadian (CIC). The student has to deal with the CIC directly for the work permit, without any involvement of the college. Among other requirements, the applicant has to produce a letter of offer from a Canadian employer.
Since the work permit is for temporary employment for up to 1 year, you must stick to the line that you intend to stay in Canada temporarily and only for the purpose of the stated employment. Once you have the work permit and temporary employment, you can apply for immigration on the basis of an offer for permanent employment.