I would think your Maurice was descended from Maurice and Catherine (Reilly) Halloran. Some of the family uses O'Halloran. I cannot, however, place him. The Maurice in the 1871 directory of Prince Edward Island (carriage builder, Campbellton Twp., Lot 4, Prince Co., PEI) would be the same in the 1881 census, in Lot 4, Prince Co., PEI. Since this last had a wife, Ellen D., I would assume he was:
Maurice O’Halloran b. Glengarry, PEI 9JAN1840, m. Ellen Donahoe (Donahue) (b. Newfoundland 15AUG1844, ca. 1846 in 1881.)
In the 1871 directory, Maurice Halloran was a carriage builder in Campbellton, Township (Lot) 4, Prince Co., PEI. Also in Campbellton was Patrick Halloran, a farmer; possibly his father?
In 1881, in Lot 4, Prince Co., PEI, Maurice was age 41, ‘French’, b. PEI, a carriage builder and Catholic. Ellen D. (35) is also given as French, was b. Newfoundland, and was also Catholic. Children were: Patrick (14), John (12), Peter (10), Walter (5), Frederick (3) and Arthur (1.) All the children were b. PEI, and all, except Patrick, were Irish. Patrick is also given as French.
Maurice O’Holloran 41, French, b. PEI, carriage builder, Catholic
Ellen D. O’Holloran 35, French, b. Newfoundland, Catholic
Patrick O’Holloran 14, French, b. PEI
John O’Holloran 12, Irish, b. PEI
Peter O’Holloran 10, Irish, b. PEI
Walter O’Holloran 5, Irish, b. PEI
Frederick O’Holloran 3, Irish, b. PEI
Arthur O’Holloran 1, Irish, b. PEI
Maurice and Ellen were also in in Lot 4, Prince Co. West, PEI in 1901, from whence the birth dates are derived.
Maurice O’Holloran b. 9JAN1840
Ellen O’Holloran b. 15AUG1844
John O’Holloran 19MAR1868
Arthur O’Holloran 17APR1880
Thomas O’Holloran 11JAN1885
This part of the family apparently used O'Halloran. If your Maurice had a son, John, who moved to Brooklyn, NY by 1870, then your Maurice must have been of a previous generation. This suggests the son of the first Maurice (and uncle to the carriage builder):
MAURICE HALLORAN b. St. Mark’s, Lot 7, PEI 24MAY1827, d. 10AUG1902, aet. 80 years, m. MARGARET SMALLMAN (b. ca. 1834, d. Richibucto, Kent Co., NB 22MAR1874)
my great grandfather, whose family used Halloran. So far as I know, this Maurice did not have a son John.
Other members of the family went to Nova Scotia, to Sydney, in Cape Breton, to work in the steel industry there; but I do not believe any were named Maurice. Perhaps your Maurice was just from NS, and may have been distantly related to the PEI family, but never, himself, in PEI.