This "Finn, Ontario" is most likely St. Finnan's Church in Alexandria, Ontario. In the church records there is a marriage between Richard O'Neil and Mary O'Neil on 20 Nov 1853. Present was Donald MacDonald and John MacLachlan. No parents are recorded. There is also a birth of a daughter Catherine 6th March 1856 sponsors were Thomas O'Neil and Mary Queogh. John MacLachlan PP. There is also the birth of another daughter Mary 5th Oct 1861 sponsors Thomas O'Neil and Catherine Campbell. J. Quinan PP.
In St. Raphael's there is mention of a Richard O'Neil and a Mary Kerevan. This may or may not be your Mary O'Neil if O'Neil was not here maiden name.