sito have you asked him for locks on the bathroom door? there must be a code in Canada's work laws that require a locking bathroom door for privacy & safety.
a solution might be to have someone go in there with you and stand guard or have them be outside....that might serve to deter him. but I would ask/tell him to please stay away...

maybe he doesn't realize how creepy he is...

& sorry but bathroom is his personal domain if he owns company so you just have to figure out a way to get him to realize that people need space/privacy..it could be in the past people have stolen stuff and brought it into the bathroom...etc. but I would talk to him..or see if he follows everyone I to the bathroom and then write a group letter with everyone's signature on it & give it to him saying we all are asking for a lock on the door for a sense of privacy.