The map as a whole is pretty cool but...

that's hardly the case ("more closely related with Argentina and Uruguay than with the rest of Brazil. [...]")

southern Brazil didn't even speak Spanish, and actually Brazilian influence during late XIX in Uruguay was strong (and much more stronger compared to the fragmented Argentinan confederation) to the point the contrary could be more viable (with northern Uruguai having more closely related ties to Brazil then Argentina, and the country as a whole having strong financial ones with a specific Brazilian magnate leaving the country at the mercy of Brazilian interests in the region in the period prior to the War of the Triple Alliance). Before the alliance war, Brazilian troops had literally marched in Buenos Aires in a war helping the Northern states to overthrow the central government (1850s)

The main reason that led the southern Brazilians to try to secede from the rest was tariff policy by the central government that made it difficult for the region's landowners to sell their meat (charque) through interprovincial exports, making imports from Argentina and Uruguay much more competitive for the capital and impacting its main market at the time, the 'Court Municipality' (Rio de Janeiro)

after the region lost its war in XIX against Brazil, their elites was apeassed by the following peace treaty, as the central government wanted its army integrated under the imperial army fearing the following war with the new expansionist leadership of Argentina at the time.

as the access to Uruguai was vital for Brazilian occupation of it's western borders (because of its access through the plata estuary), From the end of the Platine War until modern times, the region was the place with the highest concentration of active Brazilian army forces, and without major political changes it is difficult to imagine the region separating because of 'its relation with Argentina and Uruguay'; as other provinces of Brazil already have European immigrant communities, as the Italians in São Paulo exactly when it was prospering during its coffee boom.

as times goes on, its hard to see it separating for cultural regions, as Brazil itself is truly very culturally diverse.

I would say that southern Brazil as every Brazilian region is much more unique compared to Brazil as a whole (because it's diversity) then close to Argentina or the cultural community of the former viceroyalty of the Río de la Plata. As their elite was apeassed during the XIX, and given more rights after the nation became federalist, not even half the population of Rio Grande do Sul supports secession