Southeastern France is a region in France.
You can fly into either Marseilles or Nice from most major European and Intercontinental Destinations, including the US. Popular with budget (easyJet) and full service airlines (British Airways, KLM etc)
Toulon-Hyéres Airport also operates domestic flights and short haul European and African routes. Popular with some Budget airlines.
Avignon Airport is also popular, especially with budget airlines.
Montpelier Airport is also an option