If Fort Cumberland was taken then the present-day New Brunswick area might very well be American, with Loyalist Nova Scotia at its OTL boundaries. Cumberland held the small entrance to the mainland to the continent from the peninsula, and one of the major settlements in the future New Brunswick, Maugerville, was pro-patriot (indeed, most settlers in the area period were New Englander).
As for peninsular Nova Scotia/Halifax? Much harder. In those days it may as well have been an island, and as North America's premiere naval base since Halifax was built in 1749...ouch. Hard.
Maybe if the Militia Act got more people to be pissed off a riot might be instigated in Halifax proper, or a small area like the one about Lunenburg/Yarmouth, which means those places also go to the patriots (especially if Eddy succeeds in taking Fort Cumberland)? Then Halifax is ala New York n' Philly in being held by the British, but only the city, with the surrounding countryside for the Yankees.
EDIT: BTW, I'm pretty sure in some maps and descriptions of the colonial times, Nova Scotia and PEI were described as being part of New England, or about to be, or such-'New New England' as it was.