If Spain gets to the mouth of the Amazon first (they had claim under tordesillas), Portugal has little room to expand without the basin. Thats a big chunk right there geographically speaking. With control over that and Venezuela, they could easily overrun the Guyanas at some point.
In North America, you need a more stable Mexico. If the conspiracy of the Machetes (1799) is successfulI, and say it coincides with a famine like 1785, the rebels could easily get British help since theyd be fighting Spain and Napoleon. They’d be fighting for Louisiana and Florida too and would probably get them. With the British navy who knows maybe even Cuba and Santo Domingo. If you want to make it a little more spicy, you could have Spain winning the war of Jenkins Ear, extending Florida up into Georgia, Mississippi and Alabama, maybe even South Carolina and Tennesee.
If theres a Mexican American war, who knows what a victorious Mexico might take. Maybe everything west of the Rockies, splitting the pie with Canada. Maybe they get a free hand in the Pacific Northwest, they had a claim after all.
DR conquers Haiti and unifies Hispaniola, not the other way around. Spain grabs some of the more smaller islands in the Caribbean, maybe focusing more on the Lesser Antilles. Oh and this is just for fun, but there was a real possibility that Hawaii could’ve become a Spanish protectorate.