I believe Ioi said there are more than 1M preorders in USA, that means only like 600-800K has to buy it in week 1 to get to 2M.
Then it is roughly 2.8M wihout Europe, so in order for it to beat Halo 3, we would need 900K to 1M, which is unlikely.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS