The first place I'd look, if you believe they were at L'Ancienne Lorette and Peterborough, would be the parishes there. You just write a letter asking for baptismal, communion, confirmation, marriage and death records for whichever ancestors you have names/ages on. The thing you never want to do is ask for "records on the Tessier family"...there's just too many of them and no one would ever look for you. Once you get the records, you follow where they lead you. Also check with the parish in Saginaw.
The thing I'll bet donuts to dollars on is that they were in the lumber camps for a while. There's a History prof at Delta named Jeremy Kilar who might be immense help to you. He's done more research on the logging days of the Saginaw valley than anyone else and can help you identify local resources that can help you.
But the bottom line whenever you're researching French Canadians is that every record you need is housed in a parish somewhere...and there's never been a war that's wiped out any of them. Once you get back to 1799, all of the records are online at the Universite of Montreal PRDH project. The trick is just getting there with good information. Another invaluable resource, once you get back to the early 1800s, is the Loiselle Marriage Index. That's not available online, but it is on microfilm and can be ordered through Interlibrary loan and through the LDS. They're not in any good order, other than by letter of the alphabet, so it takes hours or days to wade through them. But they give the names/dates/parish/parents/parents' parishes. Thar's gold in them thar films!
Do you know which parish they belonged to in the Saginaw area? I've got some time next week and could do some snooping for you.