Agreed with a previous post.
If you are applying for a regular TRV, having medical insurance won't make a difference in regards to your visa application. Yet, it is a pretty smart idea to get an insurance coverage for as long as you stay in Canada, since as a visitor you won't be covered under any provincial insurance plan, which could be a serious issue, if it comes to paying the bills for medical services.
And here you have a choice of getting an overseas travel insurance or the Canadian private policy for Visitors to Canada. The latter would be easier to manage and cover the treatment costs for medical emergencies you may have within the country.
Here is a list of major Canadian insurance providers, what they offer and at what price -
Visitors to Canada Insurance