General information about obtaining a Canadian visa (including countries that do not need visa) can be found here.
For Non-Authors (or authors needing a hard copy letter): You will need to first register for the conference and obtain a registration receipt. Once you have registered, please complete a ComSoc Visa Assistance Request form at http://www.comsoc.org/node/add/visa-assistance-request.
For Authors: Authors can obtain visa letters by sending their information to Ljiljana Trajkovic at firstname.lastname@example.org (please include your name, paper title, affiliation and address as it appear on the travel document).
If you have any problems with obtaining a visa, please contact Ljiljana Trajkovic at email@example.com.