Arguing that the Maya and Aztecs overlap is kind of like arguing that Byzantium and the Ottomans overlap. Yes, there was some very minor overlap in the southernmost part of the Aztec range and the northernmost part of the Mayan range (if you disregard the several centuries of separation), but the heartland of the Aztec culture was in central Mexico while the Mayan heartland was in Guatamala--a long way from each other. At any rate, if we have multiple South American civs, I would prefer Native civs, but if we must have colonial civs I'd favor Gran Colombia over Brazil or any other post-colonial nation. But as I said in another thread, I'm not a fan of modern nations. Plus Brazil is just straight up obnoxious as an AI opponent.