Thank you for responding to my post and your generous offer to help.
So far, I think Belle Isle is out as the birth place of my ancestor. Last year I posted a couple queries on the France GenForum site. I was contacted by two different researchers who offered to check the Belle Isle Archives. One of them was an employee at one of the Belle Isle departmente archives. Both of them reported the same thing, "there were no Courtois' at all on Belle Isle during the period I believe Charles was born".
The birth location listed on his enlistment record in the Regiment DeMeuron states that he was born in Chambery, Savoie, France. I was put in touch with a Chambery researcher, but I only got a couple e-mails from him and haven't heard from him since October and he hasn't responded to my last couple e-mails. I think I'm going to have to locate another Chambery researcher.
They do have some of the Chambery parish records on microfilm by the LDS, but the nearest LDS library is the same driving distance from me as Montreal. So when I get the time for a trip like that I usually opt for Montreal.
If you're interested, I posted some of the information I've learned about Charles on the Cootware GenForum site. Here is one of my posts there: