Does anyone know a dentist in the Cambridge, ON region who does extractions and will bill my insurance directly?

I guess it will depend on your insurance, have you contacted your insurance company to see what dentist in that area have contracts with them.

Some policies pay better than others will have co pays and deductables

There is one at the corner of Franklin Blvd and Elgin St. in the Metro Plaza that advertises on his sign out front that he bills directly.

All I know is that my insurance covers 80% of the proceidure.

You would have to pay the 20% the insurance won't cover right then and there and I'm sure they would wait for the balance from the insurance. Don't quote me on that but call them and ask.