At Burlington "International" Airport, daily arrivals and departures occur to/from the following cities: Cleveland, Chicago, Detroit, Newark, New York City, Orlando, Philadelphia and Washington DC. There are seasonal flights to/from Toronto and daily bus trips to/from Montreal, which are the only qualifications I can think of for the "International" in its title.
It's a source of great irritation to some of us Vermonters that there are no flights to/from Boston out of BTV. For that, you have to go across the lake to Plattsburgh "International" Airport, which defeats the purpose of having a direct route to Boston slightly quicker than Greyhound "We'll Get There Whenever We Feel Like It and Stop in 46 Towns Along the Way" Bus Lines or the Amtrak "It Takes All Day and Only Gets You Three-Fourths of the Way There" Choo Choo Service.
Of course, now there's Megabus, which takes only 4.5 hours to go between Burlington and Boston. Where was this service for the past decade of my life when I was hauling ass regularly on tedious Greyhound trips that took approximately 5 years? >:(