Matter of fact, some member of my mother's extended family went down from Canada and volunteered for the South and got killed fighting in that war. I have no idea why he did that, but I imagine that memories of American invasion attempts in the War of 1812 still were strong in royalist Canada in the 1860s, so there may have been a good many people who did not sympathize with the side flying the Stars and Stripes.

On the other hand there were many who did sympathize with the Abolitionists. People from Canada volunteered for both sides in that war.