Is there a listing of what family trees have been worked on in Ontario and by who? I have been working on the Dewar Families in the County of Glengarry and often wondered who is working on what family trees and if there is a way to tie in my research with some one else.

No, but we do offer Surnames of Ontario to allow researchers worldwide to state their Ontario surname interests. Plus there are other forums that allow you to post what surnames you are researching. Paul Sheat's suggests the Rootsweb Surname Forum