BWI is now by far the busiest airport in the DC-Baltimore metroglom, largely due to Southwest and AirTran as TOLtommy notes. I figure BWI
would likely be the first choice of Canadian LCC's to the region.
is slot-controlled and no international-eligible slots are for sale right now, as far as I know. Dulles is on the far west-end of the region, and BWI
sits conveniently between both cities.
And of course, either Southwest or AirTran could decide to start flying transborder routes (or JetBlue at IAD
). I haven't read or heard anything though about plans by any of these carriers to start transborder flights. There were rumors here a few months back about JetBlue flying JFK
but JetBlue itself hasn't announced any plans.