Police are allowed to undertake surveillance of individuals in limited circumstances. 

Private communications between people, either face to face or using telephones or other telecommunications equipment, are protected against interception by the law, so long as the originator of the communication expects that only the recipient will hear it, and either the originator or the recipient of the communication is in Canada. A private communication includes a communication by telephone, internet, or other technology.

In most circumstances it is an indictable offence under the Criminal Code of Canada to wilfully intercept a private communication. The maximum prison term upon conviction is five years. Interception is not an offence if at least one party consents.

It is also an offence to disclose private communications and to possess equipment for the purpose of intercepting private communications except as permitted by a superior court judge for law enforcement purposes.

A communications provider such as a telephone or internet provider is allowed to intercept private communications for the purposes of providing service, for quality control, to manage the system or protecting against harm to the system.

A police officer may intercept a private communication without a warrant if there is an urgent risk of bodily harm. In any other situation, the police or other state agent must be authorized by a judge to do so.

The judge must be satisfied that (except in terrorism and organized crime cases) other investigative procedures have been tried and failed, or are unlikely to succeed, or the matter is so urgent that using other investigative procedures is impractical. The judge must also be satisfied that it is in the best interests of the administration of justice to grant the authorization.

To convince the judge of this, the police have to show that there are reasonable grounds to believe that a particular offence has been or will be committed, give the names and other identifying information of the people whose communications will be intercepted and other information specified in s. 185 of the Criminal Code. The authorization is time-limited, but can be extended for up to three years.