Well, I dunno about first week, but I see it as 1.5-2mil
Now, if UC2 will get to 5 mil before UC3, I see the following:
No notable "major* improvemnts - 5.5 mil
Split Screen Multiplayer Coop - another 1-2 mil
If the game is released next to another price cut - 1 mil
Bet with Dr.A.Peter.Nintendo that Super Mario Galaxy 2 won't sell 15 million copies up to six months after it's release, the winner will get Avatar control for a week and signature control for a month.