I'm thinking either carrie under wood, shakira or britney with that picture.
Longshot Miley or Taylor (I don't think their foreheads look like this)
To cover all bases a medley should include
Groups: Maroon 5 and coldplay since they've been rumored
Pop male: Bruno and Bieber
Pop female: Britney or shakira
R&B/urban pop: Beyonce or Rihanna
country: Carrie underwood or a big male star at the moment