To determine if you require a visa, you can consult the list of countries on the Canadian Immigration and Citizenship website.
Note that air travelers to Canada who do not require a visa are still required to complete an online Electronic Travel Authorization. This process is straightforward and eTAs are usually issued within a few minutes, but some cases may require several days to process, so the application should be completed well in advance of travel. The cost for the eTA is $7 CAD.
If you require a Letter of Invitation for visa purposes, follow the instructions on the Invitation Letter page.