You don't have to catch them all, just enough to make some examples. If you're not doing some kind of greyball uber shenanigans, one semi-competent police officer can close the circle on somebody pretty easily.

Search AirBnB listings in Toronto that offer "full house" rental. It's a pretty strong clue. But obviously it's not the whole picture, as you may be renting your entire house or apartment while you're on vacation.

In New York, they were scraping the website to find the short-term rentals targeted by its ban. I presume Toronto could do the same.

Let others dob them in for investigation. Home owners who are bothered are the best ones to report this.

Probably noise and nuisance complaints.