Currently there are 7 Wii U titles that have sold over 1 million units according to vgchartz numbers. With big releases like Smash Bros on the way I think it's guaranteed that there will be at least 8 at the end of the year. But here is a list of some other titles close to reaching it.

As for Monster Hunter Tri and ZombiU I see no possibility of them reaching 1m by years end. Pikmin 3 is a maybe since it still moves up by 10,000 about every 2 weeks, and a holiday boost if lucky may bring the title to 1m sold. Lego City Undercover probably won't reach it since it's been out for well over a year and seems to show no signs of drastically speeding up. One ignored title though that has lots of doubt is Tropical Freeze. Face it, it's the newest title on this list, still moves up by about 10,000 weekly, and since this will be it's first holiday season on the market, a good amount of people should take up this title. I think it will easily reach 1m. So by the end of 2014, I'm predicting 10 titles, maybe 11, if lucky 12. And by 12 I mean if Hyrule Warriors or Bayonetta 2 over performs