A Visitor Visa is required for most foreign nationals who need to travel to Canada. 

Most visitors can stay for up to 6 months in Canada. You may either need a Electronic Travel Authorization (eTA), if you are a citizen of visa exempt country. Some people are not allowed to enter Canada, which means they are inadmissible for several reasons, including involved in 
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• Criminal activity
  Human rights violations
  Organized crime
  Financial reasons
  Health