In my view, in the totality of the circumstances of this case, there is a reasonable expectation of privacy in the subscriber information. The disclosure of this information will often amount to the identification of a user with intimate or sensitive activities being carried out online, usually on the understanding that these activities would be anonymous. A request by a police officer that an ISP voluntarily disclose such information amounts to a search.
As Michael Geist points out, not only does this mean ISPs now need to change their procedures, but also (importantly) it should destroy the rationale for two new attempted bills concerning "legal access" (i.e., expanding the government's ability to get information via internet service providers without a warrant). This kind of ruling should fit equally at home with the 4th Amendment here in the US, but the issue still really hasn't been tested at the Supreme Court. Congrats up north, though, for actually recognizing the value of a warrant and just a bit of oversight on government surveillance.