Call/write MCCAP and report the property as a multi-unit/family building and request a re-inspection of the premises for changes and improvements to the property you believe (or know) took place (just in case their records have never been updated - ouch, nice tax bite!); and
Call Canada Revenue Agency and report the owner of the building (provide name and address) running an illegal multi-unit rental property and that you have reason to believe he is not reporting income from the property, apartments and/or rooms. Regardless of whether this is true or not say it to stir things up just in case he's cutting corners