I contacted Chelsea Staub through her MySpace page, and she said she will be attending. Selena Gomez has posted both in her blog and in bulletins on MySpace that she'll be at the games, and also noted that Demi Lovato will be both participating in the games and performing at the concert. A Demi fansite also confirmed this. Of course, the Jonas Brothers and Cheetah Girls are confirmed for both the games and concert. Jordan Pruitt is confirmed for the concert. We have the Miley rumor from MileyTV. I know Mitchel Musso won't be there.
Given that most of the Camp Rock cast will be there, I'm GUESSING Meaghan Martin and Jasmine Richards will attend. I don't know which members are considered principal cast though. All of them may not show up...
Also, since Selena is confirmed, I would guess that David Henrie and Jake T. Austin (also possibly Jennifer Stone) will be there. (Wizards of Waverly Place cast)
If the Miley rumor is true, we can probably count on Emily Osment and Jason Earles, maybe even Moises Arias.
As far as I know, the "As The Bell Rings" cast won't be there (with the exception of Demi).
I know someone mentioned a casting director had confirmed Cole & Dylan Sprouse. If so, Brenda Song might be there as well?
Haven't heard anything about any of the Cory In the House cast. Can't imagine they wouldn't be involved...
And then, of course, HSM3 has started filming. So I tend to think they might not be involved this year?
All total speculation... and things everyone else has probably speculated on their own, at that.
Hope it helps, but I guess we'll just have to wait and see what happens!
. I think it would be super fun to be able to have random star sightings at the park(s). No matter how it shakes out I'm excited as all get out about going. Let's keep updating and see if we can set up a meet! The DIS has been outstanding for information as well as seemingly a great group of like minded parents and fans. 
