My great great grandfather was Léon Tessier, brother of François. My great grandfather (Léon`s son), also named François, married Angéle Tessier around 1855/56 when she was 16 (born 1840). I have searched for their marriage for two years but without any luck. Lately I have started to think that maybe she was the daughter of François and Marie. My theory is based on the following facts: In the 1881 & 1891 census Angéle says that she was born in the USA; I have found other members of the Tessier family marrying cousins; I can`t François & Marie or any children in the census, nor can I find any marriages of their children (hence my enquiry).
The only explanations that I can think of are that they moved to the USA and/or they changed/misspelt their surname. Just maybe, Angéle was their daughter, and maybe your Michael was her brother.
Lots of maybe's, but unless someone else can come up with something better I feel that I have to pursue my theory.
As for your other questions, I have no information at this time. I would be interested in any Tessiers that you may find in upper New York, or elsewhere. I will certainly keep you informed of anything that I may find. Regards, Fred Sedgwick.