Argentina as we know it will pretty much just be the interior territories of OTL Argentina. Maybe Chile or an Andean state can grab it if independence for Latin America still happens in a remotely similar pattern, but it's doubtful they can hold onto it since transport difficulties and regionalisms and all. It'll be split with some state that probably includes Buenos Aires and the Rio de la Plata area--I don't see Brazil holding onto it since they had enough issues holding onto what became Brazil OTL as it was. It possibly might include Uruguay and Rio Grande do Sul as well.
Assuming the Portuguese keep the area, Chile might not be able to become independent and, maybe, Peru remains a Spanish stronghold:
In OTL, the Chilenean revolutionaries were defeated in the battle of Rancagua in 1814 and escaped to Argentina. A combined army of Argentines and Chileneans refugees crossed the Andes in 1817 and defeated the Spanish. By the early 1820s, the Spanish held Peru and Bolivia and were facing a two front war, with an independent Colombia to the North and a Chilenean army boosted by the former Argentine army enveloping them in a continental sized pincer maneuver.
Remove Argentina from the equation and, assuming a butterfly net or an ATL independence struggle, the Chilenean revolutionaries have no where to escape and enact a "Plan B" so to speak if they are defeated. With Chile, Bolivia and Peru in their hands, even if restless, the Spanish have more resources to deal with Colombian revolutionaries.
Now, assuming Spain does not fight for those territories for whatever reasons (I don't know, maybe there is no Reconquista so the Spanish part of the Iberian peninsula remains in a struggle between catholic and Muslim kingdoms while Portugal discovers the Americas and expands there? Butterflies for South America would be huge, though), it may very well be that Portugal doesn't bother too much with the region, which ought to make any settlers take a rather independentist outlook to politics and who should rule over them. A rather unruly bunch.