Back up- Cody Ransom is the backup at second base. I'm not going to profile him right now though, because I wanted to wait for 3rd base, where he will have a much greater impact with the A-Rod injury.
Prospects- Kevin Russo is the Yankees primary 2b prospect. He posted impressive stats in AA Trenton last year, hitting .307/.363/.416. He figures to be the everyday 2b for AAA next season, but if Cano goes down, Russo should get a look.