Hello Deborah, The most I know about Fays from Canada and the Brown family comes from research in Richmond, Chittenden County, Vermont. I have been told Fay from Canada is a line from Ireland and is not to be confused with the Fay family from Marlborough, MA 1648. The Fay's from Canada immigrated mid 1800's.
In 1850 Richmond, VT a William Brown 30 was found; he was born in Ireland. The Brown family married into the Fay family from Marlborough. I traced Brown from VT to CA. I've tie several lines of FAy in IL to Fays from MA but not tied many Fays from WI. Record keeping was poor in IL and WI. I've done no research in Michigan I can recall.
Your sister's dad was born between 1931 and 1936 and therefore within the last 100 years; records are harder to come by for the living. My best to you in your search for family. It must be difficult when the surname shifts from Fay to Brown, the latter being a very common name.
Thanks for getting in touch with me. If you think I can help you in some way let me know.