Most French Canadians immigrated to Michigan during the 1840-20th century. This chain of heavy migration was due to either economical or political reasons. For example some French Canadian's migrated for political reasons such as; young males trying to escape military enrollment during the 1st World War. Also rebels who participated in the lower Canadian rebellion (1837-1838). Now as to economical reasons, when one's life is miserable and one does not know how to pull out of poverty that person leaves it's environment. In this case, the French populated Saginaw Bay & Keweenaw regions in hopes of a better life and higher pay. Leaving Quebec, due to poverty, overpopulation, debt & infertile soil. In Michigan there was plenty of lumber and mining industry jobs readily available not seeking any or much experience. Some of these even allowing kids to work as well. The French were already experienced as fur traders and lumber workers, the only difficulty to face was the foreign language. Hope this helped & gave you a better idea on why they came to the U.S. :)
