The pair will both sing their winner's songs in tonight's live show as viewers vote between the acts for their favourite.
Sam Bailey's winner's song is Skyscraper by Demi Lovato, as was previously rumoured. The song had originally been recorded by Union J as their potential winner's song last year.
Meanwhile, Nicholas McDonald's winner's song is a rather less known track, Superman by Five For Fighting.
Whoever wins the show will have their song released tonight for download straight after the show, while a physical release will follow in the week.
Bookies make Sam Bailey their tip to take the crown and steal this year's Christmas Number One if she does top tonight's public phone vote.
“Sam has been our odds on favourite for some time now and these final odds are the most one sided in recent memory,” said William Hill spokesman Joe Crilly. “The X-Factor crown is almost certainly Sam’s.”
However competition for the Xmas number one could come in some unusual forms this year, with a campaign to get AC/DC on top of the charts, while novelty tracks such as the Christmas Robot could also prove to be surprise hits.
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This year's final airs this Saturday and Sunday on ITV, live from Wembley Arena, where the contestants will appear in front of an audience of thousands.
The shows will also feature guest performances from One Direction, Katy Perry, The Killers, Tom Odell - as well as Elton John, who will perform his new collaboration with Gary Barlow, 'Face to Face'.