Well, the Wii version has likely sold around 1.1mil (I reckon VGC is slightly under looking at shipped numbers), so it depends.
Will it have online? Will it be heavily advertsied? If it goes the right way, then it may reach 1.1-1.2mil in Japan. If not, it may just reach 1mil. MH is NOT as big on consoles as handhelds. Tri is by far the best selling console version to my knowledge, and I wouldn't be certain if it could outsell that.