IMO the best way for both these to happen is for the USA to take Canada in the revolutionary war (despite the normal cliche that this eventually leads to a stronger US than takes over the world), with a more powerful north and a whole new faction of Francophone papists to have arguements with I can see early federal politics being more volatile and the states have less need for common defence, and without Canada the US has absolutely no way to put pressure on Britain and so Britain might take a less favourable line towards the US.
Without Canada, what's the conflict over?