Alone the US can smash the British Empire in the Western Hemisphere. Canada would either be annexed or turned into a puppet republic (maybe a mixture of both with Western Canada going to the US and the remainder as a republic or partiationed into several states) and Britain's Caribbean islands likewise annexed, though Guyana might go to Venezuela. If the US had France, Germany, or Russia as an ally (all are possible and reasonable choices) then Britain couldn't do a thing about it.
The US (the more militaristic US I'm proposing) alone versus Britain in the 1890s would be evenly matched. US plus an ally (France or Germany or maybe Russia) would definitely win in the 1890s. The US alone in the 1880s could handedly win in Canada, but would have trouble in the Caribbean--with an ally it would probably result in a US victory. The Pacific would likewise be a territory for expansion, and the US just needs to beat the local British forces. Japan would likely aid the British with their alliance, but 19th century Meiji Japan could be dealt with a hypothetical militaristic US.
The problem with discussing alliances is the British aren't stupid and would likewise have their own alliances. Ideally, Germany+Russia+America vs France+Britain+whoever (Austria-Hungary, Ottomans, Italy) is the best, but even "Central Powers US" (US+Germany+Austria-Hungary+Ottomans+etc.) is more than enough to get a solid victory. But by the 1890s, it's hard to put a reasonable permutation of alliances together in which this version of the United States won't reasonably be able to overcome in some form.