Someone born in 1900 drops out of site in 1935. This person is last seen in 1954. You do not know if this person is dead or alive in 1999. How would you start to find out if that person is dead and where did they die.

Start with what you know. Where were they last seen? Who were their immediate relations (parents, siblings)? Track down these relations, through them you may find your missing person. Items such as obituaries, birth announcements, marriage announcements, wills, etc. may mention your missing person and their whereabouts. Try the Ontario Cemetery Finding Aid to see if your missing person is listed in a cemetery record.