I don't see this war uniting America for any significant amount of time. It was only a few years prior that we fought Mexico, which while not exactly a paragon of military prowess, it still involved quite a bit of fighting. Yet, after that war, in which we soundly defeated Mexico, the United States quickly regressed into its former ways, bickering over the balance of power.
This war would be much the same, but I've changed my opinion a little bit. I don't see the United States getting too much of Canada thru force. I see them getting Toronto and lower Ontario, and the British might be only too happy to hand over troublesome Quebec at the treaty. Manitoba and the Western provinces might go and they might not. Depends on what means what to whom. The maritime provinces and New Brunswick will remain in British hands. Why, because the British will be much better able to defend and supply a place like Nova Scotia from their major port at Halifax, and thus, the United States is more likely to face tougher and stiffer opposition from veteran British troops fresh out of India and the Crimea. By this time, Britain will cut its losses, give over lower Canada and Quebec and whatever else the US is willing to buy, and bide their time for revenge. They have the money and ability to wait it out. Any keen observer in America or in Europe would know that a major crisis is going to be facing the US in the near future. Maybe not war, but close.
Given such a major victory, like that over Mexico, the US public is highly unlikely to pay any attention to how Britain is feeling about the whole situation. Thus, Southern and Northern politicans restart the argument over free vs. slave. Canada, as abolition haven, will inevitably go free, upsetting the balance dramatically, and if this is not enough, then the election of any abolitionist president in the 1864 election, will likely start the ACW. That would be Britain's opportunity to strike.
