score:8
The way Canadian student entry works is like this. Thre is technically no such thing as a 'student visa'. When you apply to be a student in Canada you will receive:
Visitor visas are immediately usable once issued. Therefore you should be able to come to Canada at any time and be admitted (before it's expiry date of course). The length of time you can stay is determined be the immigration officer at the border. A normal stay is up to six months, though presumably on seeing your study permit they will admit you for the duration of your course.
So in short you should be able to arrive at any time before your course and be admitted. If you were to arrive an excessive time before the start of your course, like six months, you might be given only a shorter entry period, but I doubt that three months is excessive.
However the immigration official may want to ask questions to ensure that you really are just wanting to use the 3 months for tourism. 3 months is a long time from someone to be visiting Canada, and they may want to know where you are going, what you are doing, and very importantly how you are going to pay for it.