In R. v. Lerke (1986), 67 A.R. 390 (Alta. C.A.) the Alberta Court of Appeal found that a tavern manager who arrested an accused person was acting as an agent of the state. There the manager of a tavern thought the accused was a bit young and excluded him from the tavern. The accused re-entered. The manager then arrested him. They took him to an office where they searched his belongings. Marijuana was located in his coat. The trial judge found that the search infringed his s. 8 Charter rights. The Crown appeal to the Court of Appeal was dismissed. Laycraft J.A. held that the arrest whether carried out by a private citizen or a police officer was a governmental function because the right was founded upon the sovereign's power of keeping the peace. The private citizen is thus exercising the sovereign's power when arresting someone: see paras. 17 and 21.
See a discussion on this issue in Skeir (2005), 196 C.C.C. (3d) 353 (N.S.C.A.) at para 10.
In Ontario the law perhaps differs on this issue.
In N.S.,  O.J. No. 290 (Ont. C.A.):
THE COURT (endorsement):-- Assuming that the conduct of the security guards amounted to a detention, an arrest and/or a search, we are satisfied on the authority of R. v. Buhay (2003), 174 C.C.C. (3d) 97, paragraphs 25-31 (S.C.C.) that the security guards could not be considered police agents or otherwise be subject to the limitation of the Charter...
Indeed, if the actors are not state agents for s. 8 or 9, and the Charter does not protect from such gross violations of rights, surely the Charter does not extend its protection to the comparatively "mere" s. 10(b) right.
However, even in Ontario, things are not quite that settled.
Jamieson,  O.J. No. 1780 (OSCJ, Gordon J):
During an interview and subsequent telephone call, Jamieson provided written and oral statements excluded on the basis that they violated her right to silence under the Charter.
HELD: Although Jamieson's employer had the right to inquire into the parents' complaint, it knew or ought to have known that such an inquiry would elicit evidence for the police investigation. Therefore, the employer acted as an agent for the state under the circumstances, thus invoking the application of the Charter. During the interview, no indication was made that Jamieson could contact a lawyer or was free to leave. As a result, her right to silence under section 7 of the Charter was violated, and the oral and written evidence was ruled inadmissible.
Thanks to Yossi Schochet