I am also researching the Cassady/Cassidy family from Ireland to Canada, then to Vermont. My great-grandmother was Ada Cassady, born in Kingsey Falls, Quebec to Levi Leete Cassady and Mary Jane (Priest) Cassady. Levi was the son of John Cassady and Lucia Leete. It's my understanding that John was born in Canada, but I don't know who his father is, who evidentally came from Ireland to Canada. Levi and some of his siblings moved to Caledonia County, Vermont in the late 1800's.
I just obtained a Cassady Family Tree from an aunt, which has all of Levi Cassady's descendants through 1980. I am now trying to locate people in it for updates.
I have information about some of Levi's other siblings, but not much. Does it sound like we're looking for the same Cassady family?
I have found in my research that the spellings in vital records were interchanged between Cassady and Cassidy; however, the correct spelling of my family is Cassady.