Putting aside the issue of what would cause Britain to intervene against the USA in the Spanish-American War, when in OTL they allowed the US Navy to operate out of Hong Kong there's still the issue that Britain declaring war on the USA in such a situation would be seen as Britain being the aggressor.
There were incidents in which British ships going to Spain and its colonies were stopped and checked by the American navy. One of those incidents going awry is a possibility.
The Royal Navy would prevail in the Caribbean and Pacific. You might be able to get saber-rattling by the Royal Navy to prevent war, but if there is an attack on the United States from Canada, America will be willing to go through total war to expel Britain from mainland North America
Are you really sure about that? Firstly, as a debtor nation, the US had huge imports from the rest of the world pre-1915, and a loss in the pacific and atlantic will create massive economic downturn and inflation. Secondly, money from the downturned economy is needed to arm and equip the army, and around a good fifth of American industries before ww1 were held by British firms and investors, losing which will create even more economic downturn in America. Thirdly, the USA after 1865 till 1917 was a massively demobilized country. It had created a massive economic problem during the civil war that did not allow it to arm as fast without causing massive inflation and economic downturn
again, which was why the scope of full mobilization in 1917 was so heated in the Senate and House. It could not afford to arm up rapidly like it did in the Civil War, and going on a slower basis would still increase eyebrows from the entire world as to why the US would be buying so much weapons, and buy it too rapidly then the world would know something is up. Also all plans to invade Canada by the US after 1862 till 1939 involved capturing as much Canadian territory as possible, knowing they would be defeated at sea, and then return Canada in the peace for a stoppage of a blockade(most of it anyway, they intended to annex New Brunswick in such a case it seems) and then pay reparations to Britain.
Also anything that relies on Americans forgetting the Civil War, especially by the 1890s, is ASB. An estimated 700,000 to 850,000 Americans died ... that comes out to about 1 in 10 military age men
Really? In 1919 the world swore not to have a war that would have millions dead, a war in which 5% of the entire French population died, 2.8% of British population died, 1.6% of the Russian population died, 4% of the German population died, 8% of the Ottoman population died, 3.5% of the entire Central European population died, and yet after just 19 years, the countries were raring to have a round two. People may remember, governments don't, at least when it comes to putting their policies on the table.
It was total war in the American homeland. That's not the sort of thing you forget.
Tell that to the Belgians, French, Italians, Germans, Central Europeans, Russians and Balkans. They experienced total war too. America is nothing special in that regard. Tell that to Britain which was subjected to a submarine blockade in ww1 and was ready for round two in 2 decades. People don't forget. But government's often gloss over them to their own benefit.
Putting aside the issue of what would cause Britain to intervene against the USA in the Spanish-American War, when in OTL they allowed the US Navy to operate out of Hong Kong there's still the issue that Britain declaring war on the USA in such a situation would be seen as Britain being the aggressor. The Royal Navy would prevail in the Caribbean and Pacific. You might be able to get saber-rattling by the Royal Navy to prevent war, but if there is an attack on the United States from Canada, America will be willing to go through total war to expel Britain from mainland North America. Also anything that relies on Americans forgetting the Civil War, especially by the 1890s, is ASB. An estimated 700,000 to 850,000 Americans died ... that comes out to about 1 in 10 military age men. Many more were wounded. Anyone over thirty is going to remember the war itself, and people younger than thirty are still going to have have seen people with limbs missing from war injuries and know people who grew up without a father. The As far as the American public is concerned, the American Civil War was not some minor skirmish halfway across the globe. It was total war in the American homeland. That's not the sort of thing you forget.
No way in hell does the US lose.
A generation prior we were able to arm and deploy a half million men within a few weeks of Fort Sumpter being fired upon. The US would he able to conscript more men then Canada had total residents... and Britain, while mighty, has a global empire to maintain. Much like with the Germans a generation later, they can't just strip every outpost bare of soldiers to send them to the front... though the Royal Navy will bloody the American nose.
If the US wants Canada, at this point, they will take Canada... only question is how much the Brits make them pay for each mile and what the eventual treaty demands.
Nonetheless, i would agree that the USA would not loose, however nor do i agree that the USA would win. The amount of money and the economy crashed, and the amount of casualties and the very probable return of most of Canada makes it a null point anyways.