It’s Tony Bennett, I’m pretty sure it is...
It depends how much of a contrast you are looking for. If you want a more classical stringed instrument, I would reccommend either the violin, cello, viola, or bass.
As for a more typical country style stringed instrument similar to the guitar, I would suggest some more interesting instruments such as the banjo, mandolin, or veena.
The harp would also work, too!
Answer
to entertain the audience and to show the art of the movie