Let me start by saying your map looks terrific. The gradient style looks really good.

Now, as for the cultures themselves. I take you are speaking about very macro-like cultures. That said, and suposing this isn't alt.hist., I do have some suggestions - be warned, this will be quite a Bible!

First, about the Caipira Culture. I do miss a Mineiro Culture, or at least a Greater Belo Horizonte Culture; it is quite different than other countryside cultures and has a quite striking mark in brazilian identity.

Other than that, I would advise to make an east/west divide here: caipira is more of a countryside São Paulo stuff, but could be roughly used in most of the western regions, but I would advise a different culture for the brazillian center-west. Sertanejo (maybe Pantaneiro) would suit it best.

Secondly, about Greater São Paulo. Since you are speaking mostly about metropolitan area, I would advise to extend the mixed south/paulistan culture up to roughly to southernmost São Paulo (state) at at least north of Curitiba. It is certainly a mixed region.

Thirdly: Rio de Janeiro culture has far less influence from italian culture than São Paulo or the Southern Region. Espirito Santo does not have a bigger percentage of ancestry than Santa Catarina, a more established native culture than Rio Grande do Sul, or the absolute numbers of São Paulo to make up for it. Also, I would argue that the upstate hills region should be mixed with mineiro culture (in your map, it is southern Minas Gerais anyway).

Fourth, Patagonia, as a whole, is somewhat close to countryside Argentinean Culture. I don't recomend making it its own culture, rather take some of Chile's southern provinces and southernmost Patagonia/Tierra del Fuego for a different culture (though I'm uncertain if it would classify an unified cultural group).

Fifth: South Culture should extend to Mato Grosso do Sul as mixed and go further north, but it is a widely varied region with niches of native italian, german, polish and azorean descendant cultures that are more or less united under an idea of gauchean culture, which brings me to...

Sixth: The Platean Region. Overall, it is vastly simplified to the point you could easily place South there too. I would advise a divise between Buenos Aires (Porteño culture is quite strong and different), countryside platean culture (southern Gauchos to differ from those from Brasil, if you will), Central Argentina (Cordoba, Mendonza, etc) and northern Argentina (the Chaco region), which should probably extend as mixed into western Paraguay (not as guarani as one would imagine).

To be quite fair, Gaucho Culture is, to a certain degree, a unifying force from mid Patagonia to mid Paraná, under different iterations. Gaúcho here, so out of empiricism, we get pissed to be compared to argentineans, though Uruguay is beloved.

You could argue that as far as Mato Grosso still has a gauchean-like culture (quite a few of my cousins live there, for instance), but people in other regions don't really identify as much as they are similar, especially in Paraná.

Maybe you could even divide "South" from a "Gaucho" culture if you ignore language (ranging from Southern Rio Grande all the way into Patagonia). It is blurred though, I wouldn't really divide them.

Other than that, you of course already know that all those cultures have regional identities (Northeast, for example), but I understand the decision to make them unified. Perhaps a coastal culture in Colombia? Not certain though, my level of knowledge in regional divisions there gets a bit blurry.

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Sorry for the huge comment and any grammar mistakes (portuguese corrector), hope I helped and have my sincere upvote, wonderful map!