If protestors can shut down traffic downtown, and came close to shutting down the Gardiner, I don't think it too far-fetched for police planners to consider the possibility protesters could try to blockade car and bus traffic attempting to move in and out of Pearson.
For clarification, I don't mean attacking anyone , or anything. I meant blocking traffic.
Downtown, Gardiner, Pearson, subway, etc...
Or, the subway, as happened in NYC.
Over 100 protesters swarmed the Lexington Avenue-63rd Street station, at one point even jumping onto the tracks.
www.cbsnews.com
Pearson is - very - well served by GTA transit. So, no problem getting bodies there. Combine that with a slow moving rolling blockade of vehicles, with a few "accidental" vehicle breakdowns at choke points....