Actually
http://vgchartz.com/worldtotals.php says Halo 2 sold 1.7 million games more than SSBM. I don't really expect it to 'defeat' Halo 3. It deserves to, yes, but it won't. Fans just aren't as hardcore as Halo's, they consist too much of 10 year olds.
And I don't understand how you don't anticipate SMG. Have you seen any recent movies, or did you dismiss the game after the first 2?