A 2 million + first week is practically a given, FFXIII managed close to that in Japan alone and I think it will pass 3 million as well but maybe not by much.
As for lifetime sales, this is the toughie, GT games have the kind of legs that only GT games have and it is not unreasonable at all to assume that lifetime sales will be 300% of first week. Could even be more.
Its hard to align it with previous games since they always arrived in Japan first (but generally did way above 500k week one in Japan alone) but one thing is for certain; it will undoubtedly be the highest selling PS3 exclusive ever and very probably the highest selling PS3 game overall.