Well it depends, the game will be released in both the playstation network and on disc.
On disc I would say about 250k LT sales, Maybe 300k but thats pushing it. With downloads it should manage 350-400k in north america.
This game has a very low chance of becoming a million seller WW, but its cheap for $39.99.
2008 end of year predictions:
PS3: 22M
360: 25M
wii: 40M