R v. Marakah, 2017 SCC 59 (McLachlin):

[54] I conclude that Mr. Marakah’s subjective expectation that his electronic conversation with Mr. Winchester would remain private was objectively reasonable in the totality of the circumstances. Each of the three factors relevant to this inquiry in this case, place, capacity to reveal personal information, and control, support this conclusion. If the place of the search is viewed as a private electronic space accessible by only Mr. Marakah and Mr. Winchester, Mr. Marakah’s reasonable expectation of privacy is clear. If the place of the search is viewed as Mr. Winchester’s phone, this reduces, but does not negate, Mr. Marakah’s expectation of privacy. The mere fact of the electronic conversation between the two men tended to reveal personal information about Mr. Marakah’s lifestyle; namely, that he was engaged in a criminal enterprise: see Patrick, at para. 32. This the police could glean when they had done no more than scrolled through Mr. Winchester’s messages and identified Mr. Marakah as one of his correspondents. In addition, Mr. Marakah exercised control over the informational content of the electronic conversation and the manner in which information was disclosed. Therefore, Mr. Marakah has standing to challenge the search and the admission of the evidence, even though the state accessed his electronic conversation with Mr.
Winchester through the latter’s iPhone. This conclusion is not displaced by policy concerns.

[55] I conclude that in this case, Mr. Marakah had standing under s. 8 of the Charter. This is not to say, however, that every communication occurring through an electronic medium will attract a reasonable expectation of privacy and hence grant an accused standing to make arguments regarding s. 8 protection. This case does not concern, for example, messages posted on social media, conversations occurring in crowded Internet chat rooms, or comments posted on online message boards. On the facts of this case, Mr. Marakah had a reasonable expectation of privacy in the electronic conversation accessed through Mr. Winchester’s device; different facts may well lead to a different result.