I'm pretty pessimistic about Sanders after SC, so I'll say he wins VT, MN, and CO. I'm not even too confident about CO now, and the lack of MN polling is worrying as well. He should just drop out if he only wins 2 states.
For a state that has pretty liberal voting laws, the Colorado caucuses are pretty restrictive. That said, Democrats only and no voter registration at the door. You have to have been registered as a Democrat by January 4th, 2016, and 17 year olds that will be 18 on election day are not allowed to participate. I think all those restrictions lead to a victory for the candidate that has consistently won Democrats in exit polls.