For those of us whose ancestors came to Ontario between the late 1700s and mid 1800s, church records are some of the most valuable sources of information. And in nearly all cases, blacks were listed "of colour" or "black," making them easy to spot.
Bill Martin's Early Ontario Records site contains thousands of entries that may be of value to you. Even if you don't think your ancestor lived in a particular area, it will only take you a few moments to do a FIND within your browser to try to find a name you need.
I highly suggest you take a look at this site and bookmark it for future use.
Good luck in your research.
- Lisa B. Lee, PLCGS
Oakland, CA