Travel insurance is not a mandatory requirement. But about 4 years ago, there's a visitor from the Philippines who met an accident while visiting family on Vancouver Island and was slammed with $20K hospital bill. Unfortunately, she did not get a travel insurance. Yes, it is not mandatory but it will be prudent if you will get one.
As International Student, your health insurance policy starts on the first day of your school. If you land in Canada 2 months before the start of class, you do not have coverage for the first 2 months. The same thing is true with Temporary workers.
If you are a PR Visa holder, some of the Province's health plan coverage starts 3 months upon your arrival. You would want to get a coverage as well for that 3 months.
We strongly recommend that you get a travel insurance when traveling. Here's a list of trusted Insurance Agents who are based in Canada.