No spas regardless of where they are will be 100% safe. That being said, Brampton and Missisauga seem to have less activty as well as Toronto and Pickering. Vaughn, Richmond Hill and Markham have had higher activity over the last couple of years.
Wherever you go if you stick to a popular licensed spa you're safer. LE wants to get rid of the spas with underage girls, girls held against their will, any place that might have drugs and any place that is very likely offering FS. The licensed spas are trying to run a business and police themselves for the most part so the chances that these spas are guilty of the above are diminished.
I've never had a problem at the top licensed spas.