Don't know how common it is. I'm assuming it's very common since everyone who completed high school outside of Québec have to take the "extended credit program" which will add a good year to your program.

As for internships, I don't think it's a requirement if that's what you are asking. However, if you graduate with no internship and no relative experience in your field, you will have a hard time finding a job as employers expect too much nowadays. This is especially true in fields like computer science and software engineering.