Finding an address in the whole of Ontario for someone where only the name is available is very difficult; knowledge of the relevant city is a minimum requirement for a simple White Pages search. The White Pages facility for Canada is 411.ca.
If you do not know the city of the person in Ontario you are looking for, you may be able to source it from his social media profile. While few people put their full addresses on their Facebook, GooglePlus or LinkedIn profiles, many will list their nearest city, and this information will help you to find the full address if it is available from the 411 service.
If it is a person you already have a social media link to, check his profile for city details. If not, an Internet search for the name plus "Ontario" may well bring up links to social media profiles, local media articles, resumes and other public documents that list the city where he lives.
Once you have a city, simply choose that link from the 411.ca page, and type in the full name of the person you are looking for. A list of all people matching those details will be produced, though it's worth remembering that people can ask to have their details removed from such directories, so the person you are looking for may not be findable.