This is not quite accurate. PEI came a separate colony in 1769, before the unpleasantness. New Brunswick was split off in 1784 as a secondary result of the unpleasantness. Cape Breton I. was split off at the same time (not sure when it was reunited).
you’re right dtilque - sorry 'bout that - the perils of posting from memory.
PEI was part of Nova Scotia from 1758 to 1769, when it was split into a separate colony at the urgings of the proprietors (British absentee landlords): Canadian Encyclopedia, 2nd ed., p. 1753.
Cape Breton was part of Nova Scotia from 1763 to 1784, when it was split into a separate colony for Loyalists. It remained a separate colony until 1820, when it was re-united to Nova Scotia: Canadian Encyclopedia, 2nd ed., p. 358.
Some residents opposed the re-union, and raised enough of a stink in London that the British government referred the legality of the re-union to the Judicial Committee of the Privy Council (the highest court for the Empire) for a determination. The Privy Council held that the re-union was legal: In re Cape Breton (1846), 13 E.R. 489 (P.C.)