McFann in Canada

Hello, I am searching for a Rebecca McFann that married John Marshall, both of Saint John New Brunswick Canada 4-16-1856. She is listed on their marriage certificate and also on a death certificate for their daughter Sarah Letitia Marshall. On the death certificate her name is Farren and is also says she was from Scotland. Any thoughts or suggestions as to who she was and where she was from would be great. Thank you, Karen Chessa