What subregion of Latin America is Brazil in?

There is no simple answer -- the top portion of Brazil is tropical rain forest. The mostly inland southern portion is part of the temperate Rio De la Plata watershed, albeit the upper portion that is beyond the fall line and thus does not benefit from river transportation.

the southern coastal portion is very narrow and bounded by inland mountains -- this keeps the port cities from effectively communicating with the interior and is a huge part of Brazil's development problem.