Health Insurance is a mandatory part for student in Canadian life. Everyone must have a health insurance plan while the person is living in Canada, It does not matter that he/she is a student, under work permit, Resident or a citizen.
Here is some information for international Students:

As a Student

While you are attending the college, College is responsible for providing health insurance to all the students. College ties up with a private Insurance company to provide such services. After getting Insurance then a student have to communicate with the company in the case he need to be covered for any treatment, college can only guide the students how and when to communicate with the company. College is not responsible for any coverage.

As a Co-Op(Internship)

Some of the Canadian colleges have Co-Op (Internship) programs. During the co-op term of the student, the Work Safety and Insurance Board (WSIB) takes care of student’s health insurance. They cover only those health issues which occurred on the work place during the work. For a full health insurance student has to contact with the college or any private insurance company.

On a Work Permit

When students are done with their studies then they get a work permit. During this time period the government of the province in which they reside is responsible for their health insurance. Student has to contact with the province health care department for their health insurance. For such health insurances government of a particular province is funded by federal government of Canada.

Each insurance company and province have a different criteria to be covered for any health issues. So before getting insured you must check with all the terms and conditions of any health plan.