From Wiki

Ordinarily there is a three-month waiting period for Ontario Health Insurance Plan (OHIP) eligibility.

However, a member of the BE forum has discovered that it is possible, under certain circumstances, to get medical assistance before OHIP coverage begins. A member of his family received assistance with a pre-existing medical condition that was not covered by the family's temporary private insurance.

They were referred to a Community Health Centre (CHC). Normally CHCs provide family doctors to those who cannot find them (under OHIP coverage), but in exceptional cases (no clear rules defined) they also help new immigrants without OHIP.

Here is a list of Community Health Centres in Ontario.

To find out how medical insurance and dental insurance in Canada generally work, please see the Wiki article called Medical Insurance-Canada.