Do new residents or newcomers to Canada need temporary medical insurance?

Often, yes. Provincial coverage for new residents, and for Canadians moving back, may not start right away, and waits vary: in British Columbia, for example, coverage starts after the rest of the month you arrive plus two months, while in Alberta it can start the day you become a resident, if you apply within three months. The same plans that cover visitors can cover your emergency medical costs while you wait for it to start. When it starts depends on your province or territory, so check with yours.