While a united New Hampshire and Maine would lead to some butterflies down the road, New Hampshire's independence lasted a scant 12 years before being absorbed by Massachusetts Bay, and Maine held out only a decade longer. Even combined, I'm not sure they would be able to resist Massachusetts' territorial ambitions, given their position on the frontier with French Quebec, their small population, and the fact that Massachusetts was a very important colony in this period. New Hampshire shared governors with Massachusetts until 1741, and Maine was part of Massachusetts until 1820.
I suppose it's possible a longer history of unity between the two would lead them to eventually pursue separation from Massachusetts together, rather than separately. But New Hampshire had more autonomy from Massachusetts than Maine did and a brief period of separation in the 1680s, neither of which Maine could claim, and that made breaking apart easier.
Perhaps a larger Maine, contiguous with Massachusetts, never breaks apart, the voices in New Hampshire which want out get marginalized and Massachusetts today encompasses all of New England sans Rhode Island and Connecticut. Or perhaps the two colonies split from Massachusetts separately, just like OTL. Or maybe you do get a unified New Hampshire-Maine separating from Massachusetts in the 18th century. With a PoD so far back you can justify a lot of things; in the immediate time after the PoD, however, I don't think it stops Massachusetts Bay from expanding north.