No Dignum's in the Westmeath telephone book and 45 Nolan's,
1 Egan in Dublin.
1828 is getting pretty early for Ireland.
Early shipping records are scarce on line with Ancestry having the best collection. You are correct in that they may have gone through Canada as the fare was cheaper to
Canada than the U.S.
Mullingar RC baptisms 1741-1900 with these years missing
1847, 1820 & 1822 Marriages: 1737-1900 with the years 1824-1833 missing.
Church of Ireland baptisms 1849-1899 and marriages from 1739-1899