For more than 100 years Alberta law has mandated that all films must get a rating prior to being screened. If a theater charges admission, the content they show must be rated beforehand. It is expected that Detective Pikachu trailer will start showing before movies in Alberta in November or early December.
As far as the movie release date goes, Detective Pikachu debuts on May 10. The movie is based on the Detective Pikachu 3DS game published in 2016: