Hup hup hup -- no independence, no manufacturing policy, no mass industrialization in the North; the south is thus at less of a disadvantage vis a vis New England. Plus, it's far from guaranteed that the northern states would abolish slavery after getting whupped (idealism about liberty and all that likely to be a lot less popular, you know...)
Fair point and one that was on mind.
But, this might be just the thing to stimulate the nascent New Englander industry, since this war's closer to home than Britain is and will still take a couple years to crush. Witness the groth of industry in the OTL Civil War with a war effort close to home to supply. Gotta get the troops clothed and armed soon as possible, anyways, and even the OTL Dominions began to industralize in time.
Not to mention the 'north', even if you slap the border states to the south than the north to make up for *Canada being part of the *Union, is still very much more populous than Dixie. Numbers helped in the OTL Civil War and they will here.
Idealism's a mixed bag-New England's beef was on representation and taxation and if you get that solved the old amicability with Britain will probably come back, since trade and profits will quickly quelsh whatever independentist sentiments remain. And as noted, there were anti-slavery sentiments even before the Revolution.
EDIT: Beefed the post up a bit.