Fly into YUL (Montreal airport).
Rental cars are available at the airport. Alamo, Budget Hertz and much more. See the links below.
Montreal to Magog is approximately 1h20 minutes. A little more if you land in the afternoon.
It is best to fly into YUL before 4:00 PM.
You will have a room at Hermitage Country Club from May 30th to June 2nd.
Rental Car
Hertz Car Rental - Montreal Pierre Elliott Trudeau International Airport