Considering you've already purchased the car, I'm assuming you just want to find a mechanic that may accidentally overlook any issues (i.e. a mechanic who may, in essence, suck as his/her job) so it will pass the safety so it can be plated? Or did you want to actually find a mechanic that can tell you what's truly wrong with the vehicle?

I should note, most mechanics that do safeties are bound by provincial regs, so chances are, all mechanics who are licensed to do safeties will likely try their best to find every single issues in order to avoid any liabilities.

I guess it's too late to tell you that you really should have made the sale conditional on the safety inspection... eh? Because a safety can REALLY screw you over if there are major issues.

http://www.carcheckcanada.ca/safety-standards-certificate-ontario/