I think that is very likely.
It should be at 11-12M.
GT5 is probably going to be at 7-9M, with 10M a roof.
So Halo 3 should take it with a decent amount.
About best selling multiplat title, it will either be GTA IV (or later version) or some Call of Duty.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS







