Not sure why you've put this query on the Nova Scotia-Sherbrooke Co. site but I did a quick check of the Census results for that area. Below is the link for the census in the Ile de Perrot area in 1911. I just checked the ethinicity of a couple of the Dubreuil families and they are listed as Francais with the language spoken being French or English. No indication that they are First Nations.
http://www.automatedgenealogy.com/census11/District.jsp?did=...