The way I see it this game has every chance of selling over a million copies lifetime, mainly because the 1st game sold over 2 million across PS3, 360 and it was very well liked by that install base, so there's already more than a million people that may like the franchise and want a sequel.
Many people (like me) do own both of those consoles, would like to play this and don't have the factor of the 1st game not being available on Wii U holding us back from buying a Wii U to play this game (plus Wii U isn't exactly expensive), so one game doesn't have to be a system seller when you've got two in a single package for a reasonable price.
The potential install base for this game could very well be higher than 2 million because more people than those that already played the 1st game could buy it.
Wii U seems to be gaining a good line-up of titles, that when you look at the breadth of exclusives is actually starting to make it seem like a good console to complement other platforms, at least as far as I'm concerned.
