Portugal + Custom House + Colossus + Sea Goods = New Brazil(I hope Brazil is in game as a portuguese colony! Don't disappoint me Firaxis!)
The colonies will be existing civs, i.e. England, Holland, Spain will make America. It'd be interesting, however, to see what they do with civs without colonies. Maybe they'll make the civs that came after them, so Maya to Aztec, Persia to Arabia/Ottomans. I'm aware real history isn't that simple, but it's the best I can think of. There's also a problem if the 'colony' civs are already present.
Maybe it'll be a random civ?