If you wish to visit Canada you may require a Temporary Resident Visa (TRV). A TRV will allow you to enter and remain in Canada as a temporary resident for a specified period of time.
You will need a TRV if your passport is from one of these countries. Note: this link also lists passport holders who DO NOT require a TRV to visit Canada.
Australian and New Zealand passport holders do not require a Temporary Resident Visa to enter Canada as visitors.
For more general information on Temporary Resident Visa (TRV) refer to the Citizenship and Immigration Canada website.