All seems a bit too much. The UK will fight for Halifax in a very determined manner, but it is doable with a big, big ARW loss for UK. The easiest is have the USA take Quebec and hold in ARW, this gives us everything west of their. You can also do in the war of 1812, by having Napoleon do a lot better, therefore the UK can't send as many troops over. To do both, i would go with America keeps Quebec in ARW, and gains Halifax during Napoleonic wars. Or if you like later POD's, you could have the Americans fight the UK near 1860 with the forces of the civil war. You need some POD where the UK is a greater issue than the slavery issue, but that is probably doable. Think a "Kaiser Willie" type King or PM who does a bunch of actions that anger the USA but does not weaken it. Statements about reconquering the USA. Sailing RN up and down coast in threating manner. etc.