I agree with Guspaz's assessment of the situation. The most the plows can do during a snowstorm is push enough snow aside for road traffic to move, albeit very slowly. The city simply can't start taking away the snow until it actually stops falling, otherwise they'd be doing all that work multiple times.
Any amount of snow on a runway however can be disastrous during takeoffs, creating an enormous amount of drag on the landing gears. What you get is a plane traveling way too slowly to take off at all, and potentially crashing into whatever obstacle is located at the end of the runway because it couldn't stop.
I have to agree though that the lack of an effective transport system to the airport is a serious deficiency. Even when it's sunny, not having a dedicated transit way between downtown and the airport makes traveling in and out of Montreal a real pain.
The only airport I know in Canada that has a proper mass transit link is Vancouver's with the opening of the airport Skytrain line just before the start of the 2010 Winter Olympics. But even internationally, there's not that many cities with proper airport links.
One notable exception, and this is a hilarious exception, is Moscow. They've built a modern rail link between downtown and ALL THREE of their airports in just a few short years! And the fares are reasonable at about $10 for a one-way ticket!
The Russians managed to build an effective and affordable airport rail link shortly after the fall of Communism in less time than Montreal has been PLANNING their own rail link since the idea came up during the 1970s!!!--
Watch my future television channel's public test broadcast!