As we have explained, the underlying intent of Bill C-21 is not to introduce physical controls on exit. If you have travelled in Europe, you know that those controls are done when people present their passport to an officer on exiting Schengen countries. That is not the case in Canada.
If we have information that an individual will break the law by leaving the country, we could intercept them under the provisions of Bill C-21, whether they are carrying drugs or any other controlled goods. However, you won't see border services officers behind a counter at boarding gates in Canadian airports.