What about a rockier US history from the very beginning? The original Confederation briefly breaks down into chauvinistic warlordism, and by the time peace is restored, it's through a military coup. As the US expands, the parade of juntas fight federal authority tooth and nail, in order to prevent any rivals from gaining power. The Confederation of American States expands as the US IOTL did, albeit more slowly, because territorial integration can never completely happen. Ie, Louisiana is purchased by a group of rich individuals, split up between them as personal fiefs, and also serves as a Wild West for warlords who are having trouble out east [1]. States more or less act independently of the State, but often obey the Federal army simply because it's stronger. Secession is very rare, because each state wouldn't risk the chance to take control of the federal government and enforce their own will for a few years [2]. Canada becomes a much more popular destination for European immigrants, but also serves as a conduit for British-made goods into the US (protectionist tariffs and schizophrenic foreign policy make direct importation a risky venture). As Britain's industry booms during the Revolution of said economic concept, cheaply made goods flood through Canadian cities, and over-night make places like Windsor, Toronto, Vancouver, and other towns on the Lakes some of the richest cities in the Americas [3].
By the early 20th century, the US has more in common with Mexico to its south than it does to Canada, and Canada itself has developed a strong local government with significant economic power. As the old order in Europe begins breaking down [4], Canada intervenes on Britain's side and begins spreading its influence beyond North America. [5]
Only after Canada has established itself as a peace-keeping power in the 1920s and 30s does it turn to Latin America for economic reasons. Important investments include the spread of fruit companies, support of certain candidates in Central American elections, and the beginning of a canal somewhere down there. Meanwhile, the US is only just beginning to centralize, has barely any industrial capacity, and is fighting an expensive social war against the deeply-entrenched Southern power blocs that defend slavery long after the rest of the Western world have turned away from that institution, and the wreck of a nation that still endorses it.
[1] I envision this being a spread of the Feuding Southern Families archetype. Powerful aristocratic families become even bigger political powers than OTL, and often entire territories and states are traded between these families through their power-play. Almost like medieval dynasties in the Holy Roman Empire.
[2] This also results in states teaming up on the more powerful actors. For example, the Carolinas and Georgia will be more likely to work together to counteract Virginia's influence, and the New England states are almost always going to work as a bloc. State "nationality" will be fairly low, however, because counties and cities are going to be swapped between districts and states a lot more often than OTL.
[3] Probably all those cities I mentioned won't be known as they are OTL, or even be in the exact same locations; I only mean to reference the rough geography of major trade points between Canada and the US.
[4] Same process as the World Wars in OTL, although the exact circumstances as we know them would be butterflied away.
[5] More or less what the US ended up doing OTL after WW2.