Hi,
Were there any other relatives, such as inlaws, in the 1901 Canadian census living with Ellen and Horatio Seymour? Any Irish-born neighbors who might be relatives, or who may have emigrated about the same time?

Note: the 1901 Canadian census is almost entirely online now, accessible free in either English or French, at: <http://automatedgenealogy.com/census/index.html>;

If they were in Quebec, we have found Rootsweb's QR mailing list members to be extremely helpful for finding church records. Those may in turn have some clues as to which Mahoney family, or even location in Ireland. [The important advice is to always send this list a personal thank-you, even if they find nothing...] The Quebec Research website is:
<http://freepages.genealogy.rootsweb.com/~unclefred/main.htm&...;

Was your St. Michael's in Limerick a Church of Ireland parish? Earlier years' [pre-1844] LDS Batch Numbers would be one way of sorting out any Mahoney families -- at least their commonly used first names-- which may help more with the 1872 govt. required birth registrations. Remembering to Capitalize, just insert the Batch Numbers C700571 for christenings, or M700571 for marriages, in the IGI on the LDS website. There are other batch numbers for 4 other Limerick city parishes, 3 C of I and 1 Ch of Christ/ Congregational.
Contact me if any of this needs explaining.
Happy hunting,
Barb G.