Dear irish girl:
Thank you for your query to the Ireland Reaching Out message board and welcome to the site. The two surnames that you have mentioned are both in the parish of Moville, County Donegal, so that area may be a possibility for you to do further research. However, it sounds like you have a number of questions and if possible, it would be better to try to research this couple as thoroughly as possible in Canada as there may be some records there that give a location or further names (such as parents' names) to either one. Did Mary have a death record which might have listed parents? Did she have a death notice in the local paper? Any further information that you can find from New Brunswick, may give further clues and more information for you to narrow down your search. Census records can be very helpful as often, other family members came to stay with those who had emigrated previously. There may be some indication of the area or the parish that they came from.
As to the marriage between Mary and John, a search on the Roots Ireland database did not turn up any record, but not all parish registers are transcribed on this site.
You might consider creating an Ancestor Profile for both of them on the webiste under the XO Chronicles feature at the top of this page. Our members read these profiles and there may be others researching the same family as you.
Please let me know if you need further assistance.
Kind regards,
Jane