The leading case on the principles governing search incident to arrest and the scope of that power remains R. v. Caslake  1 S.C.R. 51. Caslake reviewed the restrictions identified in Cloutier v. Langlois  1 S.C.R. 158. The leading case regarding searches relating to investigative detention is R. v. Mann  S.C.J. No. 49.
Search incident to arrest. There is a common law power to search incidental to arrest. Underlying this power, traditionally, has been the need for the arresting officers to prevent the escape of the person arrested and to protect themselves by removing from the person arrested any weapon or tool that might facilitate escape and the need to prevent evidence under the control of the detainee from being destroyed. As a result of a valid and lawful arrest, police can within limits search the person of the arrestee and the surrounding area accessible to the arrestee. The arrest must be lawful. The search itself does not require reasonable grounds beyond the grounds that were sufficient to support the lawfulness of the arrest itself. The search must not be conducted in an abusive fashion. A search incident to a lawful arrest can only extend to the arrestee’s “immediate surroundings” where the lawful apprehension is effected. After making a lawful arrest, an officer has the right to search the person arrested and take from his person any property which he reasonably believes:
(1) is connected with the offence charged;
(2) may be used as evidence against the person arrested on the charge; or
(3) is a weapon or instrument that might enable the arrested person to commit an act of violence or effect his escape.
There are at least two ways in which a search incident to investigative detention is different from and more limited than a search incident to arrest. Search incident to investigative detentions is justified only on the basis of the safety of officers or the public: unlike search incident to arrest, trying to find evidence is not a permissible function of this search. More importantly, and a prior question to that of the purpose of the search, is the question whether the search is permitted at all. The power to search incident to arrest arises automatically with a valid arrest: that is what it means to say that the search is “incident to” the arrest, that no further justification beyond the arrest itself is needed. A search power following an investigative detention “does not exist as a matter of course”: rather it only exists where the officer “believe[s] on reasonable grounds that his or her own safety, or the safety of others, is at risk”