So, in a simple analysis; when you apply for visa at VFS or Visa office as the case maybe for your country of residence and the application is approved, you get a Visitor Visa counterfoil (TRV) on your passport. The Immigration/Visa officer, will determine and it will be on your counterfoil if you're issued a multiple or single entry. For multiple entry visa, you can travel to Canada multiple times and report to a Border Officer, who will determine how long you can stay for that trip. Once you exit Canada to your home country, you can travel again to Canada with the same Visa once it has not expire according to the date on it. However, you'll still report to Border officer, who will assess you and determine how long you can stay again.