In Minnesota, is it legal for a licensed real estate broker/agent to show an unlisted home to a potential buyer? Does the agent have fiduciary responsiability to either party?

Your question is difficult to answer because "listed" can mean many things these days- for sale by owner, MLS, newspaper ad, referral, etc.... I think that your asking about a fiduciary duty within this question is in the wrong context because you are not relating to a situation, or specific relationship, so there is nothing to really answer about that.