Every Song on Sia's New Album and the Pop Star Who Was Supposed to Sing It

Sia actually hasn't admitted anything about the song "Unstoppable." Many have connected Katy Perry and Demi Lovato to the track, because it sounds like the kind of anthemic power pop we've seen in "Roar" and "Confident," respectively. It's not a shot in the dark, either — in her interview with Ryan Seacrest from back in September, Sia listed both Perry and Lovato as artists whose tracks appear on the album.