I am not related to this branch but I do have the names in my tree as possiblies for some day.
My French is not that great but I looked at the marriage record from Saint Sylvestre from October 20, 1857 and it does show that William McGee, farmer. was a son of age of Patrick McGee and the late Anne McCauley.
Bridget Martin was the minor daughter of John Martin and Anna Corrigan.
Witnesses were James McGee and Michael McGee (brothers of the groom) and James Hearne (friend of the groom) plus Mary Martin (sister of the bride), James Martin (uncle of the bride), Theresa McGee (friend of the bride).
Hope this helps.