Shania will then tell them exactly what she thinks of each version. Scary!
The contestants gasped when voice coach Carrie told them the news of Shania's masterclass on Wednesday.
Carrie said: "You can sing this song for her individually. We want you to do the song in your style, your flavour, completely who you are. Present it to her - she's going to give you advice and critique."
Carrie also told them Shania probably wouldn't mind then looking her straight in the eye during their songs.
"Some of the American artists, I'm not saying who, you're not allowed to make eye contact with," Carrie said.
So the lucky four have started rehearsing madly for their special performance.