What will be the duration of a study Visa, If a student is going for a 4 year Bachelor course in Canada? How will a student can extend it?

As long as you are admitted to any university or college, your study visa will be valid. Once your course is completed, your student visa will not be valid anymore. However, the work permit can help you stay in the country legally. The post-graduation work permit helps you get a work permit for a period of equal to the duration of your course. For instance, if you complete your one year course in Canada, you will get a one-year post-graduation work permit.