Totally ASB, the Spanish ITTL could barely keep the Portuguese down and under.
Fine, let's assume the Portuguese are out of the running, that's plausible.
The Portuguese were THE colonizers. If they had as much people as Spain did, this forum would be called História Alternativa.com.pt and we would all be speaking portuguese. They were the first and the last of the colonizers, everyone else was pretty much following their trailblazing.
By comparison, the Spanish's main assets are more money and better demographics, which makes it easier to colonize and settle vast lands.
Fine, no Portuguese colonization. That doesn't mean the Spanish just swoop in and get everything.
You just opened a giant power void.
The Spanish will have different interests and methods from the Portuguese. For example, they won't be as interested in India as the Portuguese were, because for a while the Portuguese saw Brazil as just a nice patch of land to plant some sugar-cane in, while the Spanish had gold and silver coming out of the ear from Mexico and the Andes.
The Portuguese were pretty big for a good while in Indian Ocean politics. Remove the Portuguese element and you change everything there.
Fine, back to America.
The Portuguese stopped a bunch of would-be colonization attempts. Two French attempts, a Dutch invasion and I once read that a bunch of english people tried to colonize the Amazon.
Don't forget: The Portuguese had Spain at their back and... that was it. Meanwhile, the Spanish have France on their back, a far more dangerous opponent, and England will definitively be a rival - possibly allies, but possibly rivals as well (whereas the English-Portuguese alliance was always a thing, barring the Union). They also have interests in the Italian Peninsula, and in the Maghreb. Unlike the Portuguese, they can't just ignore Europe, keep Spain out and colonize more.
Also, they might end up with Portuguese colonizers, so I rather doubt we will see Spanish-speaking colonies only. Especially if Portugal is a united kingdom and not just a province, which is more probable. If they forbid the Portuguese from the colonies, that will mean less demographics for settling.
Without the Portuguese, it is rather likely that Spain has to contend with French and possibly Dutch in OTL Brazil. There is also likely to be a strong english presence eventually, and possibly some alternate colonizers.
I think your scenario is more likely to produce a more multi-lingual continent.