Nadine,

Likely your best hope of finding a knowledgable descendant of a slave from 18th Century British North America is in Nova Scotia where an African Canadian community has remained in tact since that period.

In Ontario and Quebec any of the descendants would likely be socially identified as white by now and it is also probable that any oral history would not have survived the intense racialist period of the late 1800's to mid 1900's.