Have you checked
http://d3system.com.br/category/sistemas/shadowrun/Theres an idea that never became official but yet its a good work.
I'm also brasilian, living in São Paulo and for me whatever is called (in Shadowrun setting) this spot here must be a nice metropolitan area since there's a big change that in the next few years we start to make fast travels connecting Rio, São Paulo and Curitiba, this might help to make those places to become one... even if a Carnival feathered serpent took control of the jungles we at south would be quite well with our tech based society... also never saw much about Manaus, that I take as the jewel of Amazonia, that they never made official as capital city for there but I think would be the best option.
Also the D3 idea to make Northeast South America to look like africa is quite accurate since it have a nice strategic position for piracy and stuff... yet he named that portion as Brasil but might have another name for that I don't think any pirate would care what the hell they call their turf.
Also we could have more ideas for the rest of the South South America, Chile and Argentina have those Inca culture over there, the Mayans would be within Amazonia territory but might have even more magical crap for southern side of south america yet to be discovered...
For me yet I like better to use Curitiba-São Paulo-Belo Horizonte-Rio de Janeiro as setting, they cover most of megacorp infested areas and runner heavens in the borderlines and the all mighty favelas, those are the ones I love most...
Also why no one even cared to point the future of our nice big companies, we have VALE and PETROBRAS that are some players not to be forgotten...