Is it possible to make it a crime not to have liscences ? Or some such technicality as not keeping records up to date, filing late etc
Oagre's right, the provinces can only regulate, but yes violating a regulation can result in a fine or even jail time.
I guess the question then becomes, what is "reasonable" regulation around prostitution, and what becomes criminalizing it. They could probably require SP's to be tested, buy a license to practice the trade, work in certain areas, perhaps even regulate the rates that are charged, so long as they don't stray into outright preventing people from engaging in it.
For contrast the provinces (often via municipalities) regulate strippers and strip clubs, taxi drivers, and teachers, doctors, and lawyers, as well as things like licenses for hunting and for driving a car.