Hi Fiona,
Besides BMD records in Ontario you may want to look at telephone books and other resources in the area where you think your rellies were/are. I am from Ontario, unfortunately from the other side of northern Ontario from North Bay. Many libraries carry the local phone books back to when they were 1st published as well as local family histories. I've been told that the metro Library in Toronto has many of the telephone books from many cities and towns in Ontario, If North Bay library doesn't have them that far back, the Metro Toronto Library may. The genealogy staff in Toronto and other library staff elsewhere have been very nice and helpful to me in the past in my search for rellies through the telephone books, family histories, and other resources. Hope this helps you out.
JDC