The organizing committee may request information required by them such as details of funding sources, previous visa copies, and University approval letters before issuing an invitation letter. The invitation letter may contain some of your personal information required for visa purpose as well as the reason why you are visiting Canada. The organizing committee can only issue invitation letters to the registered participants for the conference.
The conference organizers are not responsible for your visa to enter Canada. The participants are totally responsible for obtaining a valid visa to enter Canada. The only assistance that the conference organizers would do is sending an invitation letter. However, sending an invitation letter does not guarantee that your visa application will be approved, or you will be granted visa to visit Canada. The organizers cannot issue invitation letters to anyone who has not registered for the conference. Furthermore, the organizers cannot issue invitation letters to the persons accompanying with you, unless they are registered for the conference.
The conference organizers are not an authority on Visa issues, or they cannot help with accelerating the Visa process by issuing additional documents or telephone calls.
To find out whether you need a visa to visit Canada https://www.cic.gc.ca/english/visit/visas.asp