Set for some point in 2013
Although the Angry Birds Trilogy had a 360, PS3, and 3DS release last year, it looks like the Activision/Rovio/Nintendo partnership is seeing more action in 2013, as the trilogy is now set for Wii and Wii U release.
Activision announced that Trilogy, consisting of Angry Birds, Seasons, and Rio, is set to hit both consoles alongside of new content. No details are mentioned for the Wii U version, other than the fact that there will be "Wii U specific" features.
Odds are really high that it'll be severely overpriced, considering you can get the three games for a few bucks on pretty much any device.
No date is set other than a nebulous "2013" target.