I may apply for an Assistant Professor (AP) position at York University in Toronto, Canada. Since I live in Europe, I would like to know how many vacation days are available in this position. For example, what does an AP do in those weeks where no classes take place? Does the AP have to go to the office or can he stay home? Thanks for your answers!
How much vacation time an assistant professor gets is answered by the collective agreement in force at York U. According to a comment above, that's 4 weeks. These are days when you can do whatever you please. Obviously, there are constraints regarding the time when you can take this vacation, as pointed out by some comments.
More importantly your question suggests that there's potentially vacation whenever there are no classes. So for one thing you may need the time between semesters to develop your teaching material, but also an Assistant Professor is not a teaching-only position, it's research/supervision + teaching + typically some admin duties.
Finally, note that in many Canadian Universities there is a summer term with classes going on between may and August. So you could very well end up teaching all year around; there's typically about 3 to 4 weeks between the end of classes for one term and the beginning of the next (and that time includes exams and marking).