3 3-hour exams in a row with no time in between. What can I do?

Whether this is a standard practice or not highly depends on your university. However, the attribution of these exam period is an automated process and some situations like yours are bound to happen.

If I were you, I would consult the specific rules of your University. I know at that my previous Canadian University in Montreal (École Polytechnique), there was a rule that limited the amount of exam hours you could have in a 24 hours period, ( I believe it was 6 maximum per day). If such a thing occurred, you could ask for the exam to be moved as this was judged to be unfair.

You can also consult with your student committee (of your department or your faculty) and your department since you say that you are following a standard path. In that case, there will be many students in the same situation and they should prove to be understanding. The student committee can usually present a uniform front and defend the entire class as a whole concerning this issue. There is absolutely nothing impolite about this if you proceed politely and you act as soon as the semester begins. The sooner you handle this issue, the easier it will be to solve.

I believe you are right in saying that this will not allow you to perform to your full potential, and you are right to ask for a more humane schedule.

I do not have experience in Canada, but I cannot imagine a university anywhere doing this intentionally. It's very easy to see how it could have happened unintentionally.

I would reach out to the professors as soon as possible after receiving the syllabus. The reason I say after is that one or more of the professors may already be planning to hold their exam outside of the regular schedule. Explain the situation to the professors, as well as the fact that you believe a large number of students are affected.

The professors have just as much interest as you do in the exams being an accurate test of your ability, and I cannot imagine they are happy with the situation. They're the ones who either 1) have the clout to get the administration to reschedule, or more likely 2) have the ability to schedule an alternate time.

Finally, an anecdote: This happened to one of my courses back in undergrad. The administration was unable to reschedule the whole exam because it would have given some people two exams at once- the professor was apoplectic. He eventually scheduled a second sitting of the exam- one open to those who had a conflict.

You might want to bring this up with one or two of your professors - show them the curriculums and the times you have tests scheduled, and see if you can work something out with them so that the times don't run into one another.

It's entirely possible that the professors don't expect students to take these courses all in a row, so you might just be unlucky - but it's also possible that students aren't supposed to be taking all these courses at once (perhaps a mistake in setting up your curriculum), and a professor could spot that right away.

At the very worst, you'll find inflexible professors who refuse to help you - and it'll be no worse off than if you hadn't tried.