Sunapee, NH is a small ski and lake leisure town. Due to its small-town location, if you are flying in, the most common way to get from the airport to the Inn is by renting a car. 

If you fly into the Boston airport, there is a shuttle service via Dartmouth Coach that can take you to New London, NH (~20 min drive from Sunapee).
107 miles, ~2 hours from Sunapee, NH.
A car rental will most likely be necessary. You can find cheap options through Kayak, or by calling any rental company near the airport.
116 miles, ~2 hours from Sunapee, NH.
143 miles, ~2 hours from Sunapee, NH.