Dig out your address book and Christmas card mailing list (and those of any relatives you do have contact with). Doesn't matter how old this information is, it'll give you a place to start.
Use http://canada411.ca to see if they still live at the address. If not seek out city or phone directories for that place starting with the year of last known contact.
Use http://canada411.ca to cold call possible relations. Look up person(s) that share names of relations or those with their surname in their last known place of residence.
Get in touch with the genealogy societies where your shared ancestors lived. Inquire if anyone is seeking your shared ancestor.
Put an ad in the newspaper of their last known residence.
Track down deceased relations and use that information to find the living. Obituaries are fantastic resources and some cemeteries or funeral homes may be willing to act as an intermediary and pass along a letter from you to next-of-kin.