I suggest you to go through this where they explicitly list the conditions to be exempt..
https://www.cbc.ca/news/canada/windsor/border-ticket-tunnel-quarantine-act-1.5926311
It clearly says exemptions are based on travel pattern (daily or weekly) as I said before and not based on industry someone works. It's pretty much what I have been saying.. CBSA or Canadian government understands that they cannot restrict people from going to their work.. if someone says they want to go, they will have to go. Government cannot peek in on what they do for work. This covid test requirement is going to make things counterproductive. Many people who are traveling monthly might now plan to travel weekly to avoid testing in Detroit.
They should exempt anyone coming under 72 hours through land borders and test them on entry because covid tests are anyways 72 hours old someone going out from Canada could catch even after taking the test.