I don't think the Trilogy is going to sell especially well on any platform, but I imagine it would do the best on Wii U, at least proportionally to the install base, because the series has never been on a Nintendo platform before. People who wanted to play it on 360 and PC already did, and I wouldn't be surprised if picking up copies of the individual games on PS3 were cheaper than the Trilogy; 2 and 3 are already sub-$20 on Amazon.
Much of this is true for me and, I submit, for many. I have not played the trilogy but I would like to. Why? well a buncha reasons. Here are 5:
1. I don't own a 360.
2. I don't play PC games. I game on consoles. I know I could set it up so I could play on PC but, for many boring reasons, this is not happening.
3. I own a PS3, but then I could only play 2 and 3.
4. These games are, reportedly, each huge spawling time-consuming games. I want to get around to them but I have to consider the "right" time to do it.
5. I would be delighted for the trilogy on Wii U. I would buy that. I probably will not buy just ME3.