Well, the POD for this establishment of Los Estados Unidos de las Americas could simply be the Spanish/Castillian/Aragonese/Whatever winning its civil war with the Provinces of the Low Countries, thus preserving its naval and economic base. Spain then proceeds to kick Japanese and Korean ass to include them to the Spanish East Indies.
Somewhere along the way, the Spanish countries managed to get themselves in personal union with Norway. Meanwhile, the Low Countries are now becoming too much of a trouble for all they're worth, so they granted them independence, but not before plundering their treasury and transferring most of their navy to Spain (just like what William III did for England OTL).
But that money eventually ran out in the long term. Due to the danger of bankrupty in the late 1890's, Spain decided to sell the Philippines to Britain for a cool amount of cash.
Fast-Forward to 1930's with the Spanish Civil War (ignoring all butterflies outside the Spanish Empire), with the Nationalists and Royals winning the war in Spain, while the Republicans seize the colonies (and Norway).