Unless you have a particularly complicated issue you could simply apply yourself directly with CIC. All the guides and forms are available on-line to download and it would be much cheaper for you.
Otherwise if you feel you must use an agent, you should know that Migration Consultants and Lawyers must be registered either with the Canadian Society of Immigration Consultants (CSIC) or with a law society/bar of a Canadian province.
Go to the CSIC website here http://www.csic-scci.ca/find/
to search for agents both in and out of Canada.
Hope that helps.