Should do OK in Japan. It's a high profile brand. But when even FFXV struggles to hit 1 mil I don't know if I can say "it will easily break 1 mil". I think we will know more after TGS (assuming there is anything to show by then).
So, let's say to does 1.5 mil in Japan (does anyone predict it will do more?). To hit the expectations of a Monster Hunter game it will need to do an additional 2 mil worldwide. That's assuming that MHW costs the same to make as a handheld title, which it almost assuredly does not.
Let's predict! Do you think those numbers are possible?