There are different types of visas available for visiting Canada. What you need will depend on where you are from, how you are travelling, and what documents you are travelling with.
Information about entering Canada can be found at the following web page :
Entry requirements by country or territory – Canada.ca
Most people require an eTA, which costs 7 CAD; details can be found at the following page (with a link to the application form):
Electronic Travel Authorization (eTA) – Canada.ca
It is the responsibility of conference delegates to ensure they apply for and obtain an appropriate Visa before travelling.