Given that AA already holds 50% of all US carrier frequencies between the US and GRU and will gain yet one more with the merger with US, it will take a COMPLETE absence of interest by every other carrier for AA to gain another frequency, which is highly unlikely to happen.
It gains nothing from the merger, because US only has a leased slot that will return to UA in, IIRC, 2014.
Furthermore, if AA ends up proposing the only West Coast-Brazil service on a U.S.-flagged carrier, it's not difficult to see why it has a very good chance.