The government transferred the responsibility to the airlines so they're probably the ones getting a fine. The airline will deny you boarding without the covid test and the ArriveCAN app. Some airlines are checking for the hotel reservation as well but that can be easily forged.

I travelled back to Canada from the US a few weeks ago and the airline checked the PCR test at check-in (they don't issue you a boarding pass with online check-in) and at the gate they checked the test again and the ArriveCAN app.
I didn't have a hotel reservation and the airline didn't care.