Have you gotten any leads yet from your posting on other sites?I hope so.I've been looking inthe Fortin family but only mildly in search of the descendants of my gggrandfather's sister who married into the Fortin family once the Prefontaines had left Quebec.
One piece of info that I picked up doing this is the possibility that the family name youare looking for is Fortier.Have you looked into that family name?
On another note, you mentionned the Fournier possibility.Interestingly enough, the original family name for the Prefontaines was Fournier (Fournier dit Prefontaine). All descend fromthe same individual, one of many Fourniers who came to New France, but the only one who was attributed the military name Prefontaine. He setteld in Longueuil, onthe south shore of the Saint-Laurence across from Montreal.