I doubt that Brazil would try with the Spanish Empire alive and a Rio de la Plata that without the chaos of independence is most likely experiencing a strong boom thanks to trade.
On the flip side, Brazil is also much stronger than OTL, without the Court leaving Rio and without the costly Independence War that practically bankrupted the early Brazilian Empire. There will be some trade in the Río de la Plata, I believe, but Rio de Janeiro could remain the primary destination for commerce in South America, especially if the Opening of the Ports still happened.
In this scenario, I see it more likely that Brazil will try to create an internal division between the eastern band and the rest of La Plata over the coming decades.
That's a possibility, but it's important to contextualize things: Portugal had wanted control of the eastern margin of the Plata ever since the 17th century, that's why they founded Colônia do Sacramento there and also founded Montevideo (which was later destroyed and refounded by the Spanish).
That is, without the instability of the late-1810s and early-1820s in Brazil, the Portuguese Court in-exile is much better prepared for a conquest of the Banda Oriental than IOTL and without independence, it may be able to hold it instead of the Empire which lost it in the Cisplatine War due to a conjunction of factors (Defeats on land campaigns and the Confederation of the Equator revolt, in which thousands of soldiers were mobilized and were kept in the Northeast for "pacification" purposes and most importantly the refusal of the Brazilian Parliament in funding the war as a protest of Pedro I's closure of it during the 1823 constitutional assembly). None of this (except MAYBE land campaign defeats, but even then I doubt it as many experienced Portuguese soldiers will remain in Brazil ITTL) will happen ITTL.
IF Portugal-Brazil conquers Uruguay, that might once again create new independist feelings in the porteño elites as they would believe that Spain wouldn't be prioritizing their security, which could: a) Result in an independence war or at least a major anti-Spain revolt in Buenos Aires or b) Result in a war between Spain and Portugal
EDIT: Also, if this map is not wrong, Argentina is
already independent