As pointed out by several others, there isn't really a need for the Roman Empire to colonize Brazil because the resources that are needed for that, would mean that it probably controlled large parts of the Eastern and at least part of the Western Mediterranean. And as stated, the Age of Exploration and the subsequent discovery of America were all in search of another way to India and China, so with the RE controlling that large of territory, the trade with India and China would pass through its own territory or it's merchants would trade directly with India/China. If the RE would colonize it would be in the East, not the West.
The only way that a colony might happen is pure luck.
The Goths settling in the Balkan instead of moving into Italy which provides the RE with manpower for its army, the Justinian conquests succeeding quicker and less brutal, especially in Italy and don't utterly devastate the countryside and cities. With that extra manpower and money, the RE recovers from the Plague much better. The Perpetual Peace might last for way longer than it did in otl, giving both sides to recover and maybe even seek out better relations against each other. the rise of Islam might be countered or even completely avoided and the RE holds on to all the Justinian conquests. Several centuries later the RE still controls the Eastern Mediterranean, Italy (and islands), Carthage and hinterlands, Iberia. Overpopulation might have some crazy dude search for new or better places to go, eventually discovering a new continent to the west,
