In Brazil everything is bureaucratic and complicated. In order to fly a brazilian registered airplane you need a full brazilian licence. It's not something you can do in a few days time frame.
I don't know exactly the process for conversion, but you need a bunch of docs, do a medical check in a credited brazilian clinic and also need to do 2 flights (one being an adaptation instruction flight and the other a checkride) and pay some taxes.
Aftter that you'll have your licence converted to a brazilian one. Speaking like that it might be simple, but it's not.
It's written in portuguese (Google Translate may help), but here is the official source from the ANAC (Brazilian National Civil Aviation Agency) website about licence conversion:
Validação de licenças/habilitações estrangeiras. ? ANAC
On this website there's a description (Google Translate might come in handy once again) of the whole ordeal that a brazilian pilot had to go through in order to convert his FAA CPL into a ANAC CPL.
Convalidação FAA-ANAC: um caso real ? Para Ser Piloto
And after doing all that, hiring a C172 for flying around in Brazil is not no easy too. Not many options available I'm afraid.
There's a famous saying: "Brazil is not for beginners"
Anyway, if you need further info just ask.