It's been almost 5 years since I last had any involvement in this process but at that time it was as follows.
Send a letter to NavCanada requesting that your C registered aircraft(s) be excluded from inclusion in commercial 3rd party flight tracking data. They in turn send the request to the FAA as that is where the 3rd party flight trackers get their data. You may have to provide some proof of your authority with relation to said aircraft(s) as well as some reason for the exclusion.
The added complication these days is the proliferation of antenna's by such commercial websites as Flight Radar24 that don't rely solely on ATC radar to generate their data. Not sure if or what the options for exclusion are for that.