Know about the company: founded in 1996, took over from Transport Canada. Private, but not-for-profit, funded by user fees (airlines pay a lot, private plane owners pay a little). Provides all ATC/FSS services in the country (with one odd exception that probably doesn't matter), but does a lot more than that. It is also responsible for designing, testing and maintaining nav aids and approaches, publishing aviation charts/publications, disseminating aviation weather info. Works with other providers/companies on initiatives like ADS-B and launching the Aieron satellites. Know about the Flight Information Regions. Know the name of President/CEO.
Streams are:
IFR - considered the most challenging and in general best paid. You sit in a "dungeon" with dozens of others, only look on the radar, and help direct a/c in terminal, low-level or high-level airspace.
VFR - sit in a tower, use a combination of visual lookout and radar surveillance to separate a/c in the control zone and help them out a little bit beyond. Considered a little easier than IFR, though it's in part a personality preference. And this doesn't apply to Pearson tower, by far the most challenging unit you could be assigned to in any of the 3 stream (judging by the pass/fail rates)
FSS - not a controller, but many duties are similar. You could be in a "tower" at an airport or in a room with no windows. You pass info along to a/c, including weather conditions, IFR clearances relayed from IFR controllers etc. You can't tell them what to do, but you can provide info, updates and suggestions to ensure everything runs smoothly. Easiest to qualify at, least pay, guaranteed to be away from major centres. Some are truly in the middle of nowhere.
Know the basics of how training works - first generic/basic classroom portion and sim, then on-the-job training at an actual unit handling live aircraft.
Look up basic HR behavioral questions, there will be a couple.
You might be asked to demonstrate some VERY basic knowledge of aviation. Like, name five airlines, five airports and five aircraft types.