For Canada Immigration, a representative is someone who has the permission from the authorities to conduct business with IRCC on behalf of those who want to immigrate to Canada or those seeking Canadian citizenship. The services of a representative can be paid or unpaid. The one who has appointed a representative can also authorize IRCC to share any information on their case with the representative.
The Citizenship and Immigration laws of Canada covers such representatives comprehensively and have a well-defined terms of the services mentioned in the law. It is the responsibility of the prospective immigrant to look out for an authorised representative while taking its services for the immigration.