what game will break record 1 day, 1 week?

[Soleron]

The next major Pokemon game, on a successor to the DS.

VGChartz says:

Pokemon Diamond/Pearl Week 1: 3,559,092
Halo 3 Week 1: 3,815,444

So it wouldn't take that much of an improvemnt over D/P (and there was plenty that could be better) to get 4mil week 1.