A interesting aspect could be if Habsburg after annexing it, decided that only subjects from their German possesions could settle there, much as they had as a rule with Castilians in the rest of the Spanish New World Empire. They would kept it seperate from their other possesions. If this policy is kept in place until the Spanish Habsburg goes extinct, we could see Austria gain it together with the Spanish Netherlands. If Austria first have it as a possesions at that point it's unlikely to be lost again unless it rebel. But population-wise, it's going to have so low population until 1900 that it's unlikely to rebel, through it will likely see a greater German immigration, so it may be a little more developed. If we imagine a low butterfly world, we would likely see USA invade it in 1917, and setting it up as a independent state. Today the world would be little different, except for the existance of 25-35 million strong German (likely High German with heavily Flemish influence) speaking state in Latin America.