Any classical music is suited to cello. Popular music is probably better for a guitar or a piano, but anything by Brahms, Bach, or Mozart will sound lovely on cello. I like Minuets and Etudes, but I have been playing for a while.
Flyleaf songs aren't normally played on the cello, so I doubt there is sheet music or anything published. All I can is, try to hear it out, and write it down. Then you can work on it until it meets...
If they are transposed to a higher register, cello pieces can easily be played on the violin. However, the tone color between the cello and violin are very different, so many cello pieces would not...