This is the issue that has been bothered me since 2002 for travelling as I have no control of the others! Personal hygiene is most important especially on public transport, airport and bus/ferry terminal. Sanitation pack and mask in my day pack.Whether it's diving or anything else, you can be as responsible as you like, it's the irresponsibility of others that will get you into trouble.
And I might have to consider wearing mask from now on in those mentioned places. What have I got to lose?
Good luck Canada