It is only confirmed he will help Walsh during judge's houses, nothing about performance.
By the way, he posted all the song titles on his Facebook, but they aren't in the right order:
Baby Let's Dance
About You
Coming Home
In The End
All You Need To Know
When I Met You
Knee Deep In My Heart
One Of Those Days
Always Tomorrow
Everything's Gonna Be Alright
Everytime
Everything To Me
You and Me
Of course, this is only the standard edition, the Deluxe will have 2CDs so we can expect more songs. He also revealed he recorded the acoustic version of What About Now when he was in Manila, so maybe he will release a few more Westlife tracks for the Deluxe edition.