Ordinarily a job offer is an absolute requirement before obtaining a work permit. That's how the system works and why most Canadian employers won't even think about hiring foreigners. It's too much trouble.
However, since you're still in school but soon to graduate, I think you qualify for the "working holiday" visa. It would allow you to work for up to 6 months. That might give your prospective employer sufficient time to evaluate your 'worth' and try to overcome the work permit bureaucracy.
http://www.swap.ca/Click "Swap To Canada."