To locate a specific telephone number in Ontario, Canada, use the government-produced phone book or Canada411.ca. Phone books are still delivered to all residential addresses in Ontario, as of 2015, though most phone books are specific to the municipality and don't have a province-wide registry of numbers.
All publicly registered phone numbers are available online through Canada411.ca, the nation-wide online telephone book. Anyone can request an unlisted telephone number and cellphone numbers do not appear in the phone book. You can try the Reverse Phone Number Lookup feature on the home page of Canada411.ca if you know the number, but not the person with whom it is associated.