Auckland and Wellington should get the first two games against the strongest opponents. Hopefully they are thinking big and they open with NZ v Samoa at Eden Park.
I think Christchurch should get the third game. They were dudded with the trans tasman test in 2011 because of the earthquakes and the last high profile league game in 2010 got 21k in horrible conditions so the appetite is there. Canterbury Bulls are the current NZRL premiership champs as well. AMI Stadium is 18,000 in it's current configuration but temporary seats can be added to push that up to 25,000. The Warriors and Penrith are taking an NRL game there next year so that can be the litmus test.
Forsyth Barr is a great stadium, but the attendance was beaten by Whangarei in the four nations last year with a higher profile fixture. The students will have left by that time of year and the majority of the crowd will be coming from Christchurch and the West Coast anyway.
For the group games not involving NZ I'd be looking at Mt. Smart, Hamilton and Whangarei...it would be nice sentimentally to have a low profile game in Greymouth as well, not very practical though.