The meaning of possession of electronic files has been established by the Supreme Court of Canada in R v Morelli  SCC 8. This case concerned allegedly pornographic internet files. Central to the requirements for possession is the concept of control.
The Court split 4-3. The minority made much more use of case law than did the majority, and the majority relied more on fundamental principles. The majority held that knowledge is a requirement for control, and that control is not constituted by the mere viewing of an internet file. Control requires knowingly acquiring the underlying data file and storing it in a place within one's control. The mere automatic caching of an internet file does not of itself amount to storing it unless that caching occurred with knowledge that the file was retained.
The minority regarded control as existing when the accused willingly took or maintained the use or benefit of the material, so that it did not need to be on his computer's hard drive.
In this case a search warrant had been obtained without sufficient grounds (as held by the majority) and the evidence had been obtained improperly. Applying R v Grant  SCC 32 the majority held the evidence to be inadmissible.