Ralph Connors: I did find a probable marriage record for John Cahalan and Mary Spain, in 1847 at Notre Dame (Ottawa). It's in the Drouin Collection, on Ancestry.com: July 2, 1847, John Cahil and Mary Spain, [no parents' names given], witnesses Elizab[eth] Spain and Pat[rick] Maloney; M. Molloy, priest. In another part of the Drouin Collection is the reference to Bytown as their residence at that time, and his name was written as John Cohal.
I have not yet determined where they lived at the time of the 1850 and 1860 censuses, and I have not pursued her birth/baptism in Ireland (Tipperary?). Thanks for your reply last year. Eva Murphy