Canada welcomes millions of non-immigrants as visitors/tourists each year apart from individuals applying to work study & settle.
Visitors for Canada need to apply for Temporary Resident Visa (TRV).
Validity of visitor visa depends on the type of visa. It could be Single Entry which is valid for 6 mths, Multiple entry visa with duration of 10 years where maximum length at one time is 6 mths.
Some countries have been visa-exempted by Canada for those intending to travel by air. But need electronic Travel Authorization (eTA) to come here.