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The US under Seward's Foreign Policy tried to gain British Columbia from the British in the late 1860s, but ultimately that did not pan out.
What if the US had been able to gain British Columbia and the boundary was set along the continental divide? As far as Pacific bases go, I think Britain either retains Vancouver island or strikes a deal to gain influence over Hawaii. The US meanwhile has to drop the Alabama claims and pay the British a pretty penny. Maybe the border is adjusted elsewhere in Britain's favor (48th or 47th parallel east of the rockies? Northern Maine? Islands in the Great lakes?)