A duo is a lovely smaller alternative to a quartet or trio. For modern pop songs, it’s a great idea to pair the violin or cello with a chordal instrument such as a guitar or keyboard. The rhythms and harmonies will sound upbeat and full. You can also try a saxophone for a cool, modern, jazzy sound. A violin and cello together sound classical and beautiful.
For Canon in D, A Thousand Years, Can’t Help Falling in Love, and All of Me… any duo will be beautiful!