South Terminal.
They don't currently fly from Gatwick.
South Terminal.
South Terminal.
North Terminal.
North Terminal.
North Terminal.
North terminal
Easyjet and British Airways both fly to Nice from the North Terminal Monarch fly to Nice from the South Terminal.
British Airways fly to Barbados from North Terminal.
London Gatwick (LGW) -> New York/Newark (EWR)
Virgin fly from gatwick direct to Las vegas.
At the time of answering this question (13th November 2013) there are no Virgin Atlantic flights currently flying between Montreal and London (both Heathrow and Gatwick).