Trudeau said, clearly, that this fee would apply to non-essential travel. Of course, since no details have been provided, we can all ignore that he literally said that since there's no proof.One possibility would be to waive the fees for people travelling for non-discretionary reasons. That way it would only apply to people travelling for discretionary reasons.
I could easily show my work visa and termination letter to show that my travel home is non-optional. People popping in Mexico for a vacation could not.