https://www.attorneygeneral.jus.gov.on.ca/english/private_prosecution.php

Generally, allegations of criminal activity are reported to the police. After the police investigate, they may lay criminal charges. However, anyone who has reasonable grounds to believe that a person has committed an offence may lay an information in writing and under oath before a Justice of the Peace.. . .

This website appears to have good information:

Canada: Private Prosecutions How To (original link not working: https://member.suewrongdoers.com/research/canada/canada-private-prosecutions-how-to/)

Private Prosecutions are a way private persons can lay charges against anyone, including “officials” of any kind, who are involved in wrongdoing (always have a legitimate complaint and evidence first). Often charges are not investigated or prosecuted by officials, against officials, so a private person can lay charges themselves.