Hard to preditc.
Very first MH that started all this MH madness in Japan was MHF for PSP, which initally show no sign of being a million-seller (exactly the same sales first week like it predecessors), but eventually got legs and... 1M. Since first success of MH series came out three games: MH2 for PS2, MHF2 and MHFU for PSP. All games got serious boost in sales comparing to first two titles: 370k (MH2, PS2) -> 740k (MHF2, PSP) -> 860k (MHFU, PSP) - those are first week sales. So as you may see even PS2 version sold relatively good, but for some reason haven't got legs and despite of strong first week sold worse than first MH for PSP, which started only with 120k in first week.
Capcom definitely trying to transfer MH series succces to home consoles. As you may know they're going to port MHG from PS2 to Wii (MHF on PSP is a extended port of this game), building up MH fanbase on Wii console. So I assume after release of MHG on Wii we may predict MH3 sales quite accurately.
Until that time I doubt it will be such a success as MHF2, MHFU, but at the same time MH3 could do a lot better than all PS2 games and even MHF. So I'd say up to 400k first week, around 1.5M life-time at least.
Hm, you got the point, BUT... why do MH2 on PS2 with strong first week sold only 630k according to VGChartz? It should have done twice as that.
