http://www.cic.gc.ca/english/information/representative/faq.asp
What could happen if I do not inform Citizenship and Immigration Canada (CIC) that I paid a consultant?
It is against the law to give false or misleading information to the Government of Canada. If you choose not to disclose the name of your consultant to CIC or the Canada Border Services Agency, your application may be returned or you may be refused entry to Canada.
Immigration consultants who advise you to provide false or misleading information are also breaking the law.
Under new legislation in Canada the above can result where a representative is used who is not disclosed.