I'd say it will be something like this ...
Wii U 30-40 million (closer to 40 if it can get big titles like Smash Bros. out this holiday or holiday 2014).
PS4: 50-90 million
720: 50-90 million
I put a wide range on PS4 and 720 because we just don't know enough about them to make any kind of accurate predictions at this point ... 720 hasn't even been anounced yet. Leaning towards one or the other would just be personal bias talking. Sony has not announced all of the features (or even shown for that matter) for their console, and Microsoft won't tell us anything until May 21st.
The Wii U is already here so we can make safer predictions about its final sales, and there are still a lot of things Nintendo can do to change these numbers (look what a dramatic price cut and lots of quality titles did for the struggling 3DS). I fear that Wii U may be destined for low (Gamecube style) sales if Nintendo does not introduce a major price cut along with solid titles. 3rd party exclusives are not necessary in my opinion. A price cut and a bunch of solid first party will be more than enough. Improving and expanding their online capabilities for the WIi U would be a nice idea too (add accounts that aren't tied to the system, cross game chatting, achievements, have the same DLC available as competitors, ect.) Unlike last gen, Nintendo should get most if not all of the third party games that Microsoft and Sony will have (maybe not EA ... at least not yet though).