Hi,
The thing about country level TLD's is they will rank well in that country, If you use a .com.br domain it may not rank well in Australian results or USA results only for the brand term, even if you geo target sub folders on the domain.
Can you acquire the .com domain? From my experience .com works the best on a global level.
My advice is to use the domains you have for specific markets on the CC TLD's yet for other areas which you are not able to acquire the domain use SUB FOLDERS on the .com domain and then GEO target these sub folders in Google webmaster tools.
Finally do not use sub domains it is not a wise strategy, you will have no internal linking value.
