Short answer: KZ2 easily
Long answer:
Don't use Halo wars as a comparison as it's a RTS and till now no RTS has managed to sell even a million on a console...KZ2 is a shooter and needs to be compared with other shooters.
To me in its 1st year KZ2 has to sell at least as Gears of War (first one)...both are (or were in the case of GeoW) ultra hyped game and PS3 can now count on a 20M userbase (vs 6M X360 at the time of GeoW's launch).
This thread is full of damage control: for KZ2 anything under 4M in its first year would be somewhat disappointing given the hype surrounding this game (big shooters any given year manage to achieve this result and you can't consider KZ2 just like "another shooter")...on the other hand anything over 2M (1st year) would be simply exceptional for a RTS no matter the name it brings (that would be more than double than the best selling RTS in the history of console gaming)
44.2 M 
27.1 M 
20.8 M
