Here are my thoughts:
1. Rental Car Insurance - Your current US car insurace (GEICO/Progressive..etc) is valid in Canada only if you are a visitor to Canada. The moment you complete your landing formalities, you will be considered as a landed immigrant/ resident of Canada. In such a case, your insurance company will have a substanial reason to back off from the insurance claim, if any.
Advice: When you rent a car, ask the car rental company for insurance and also tell them that you are travelling to Canada. Just to ensure that the insurance is valid in Canada also.
Health Card: Generally Health care is managed by individual Provinces/States in Canada. When you apply for a health card, they ask you for address proof of that province. In my case, I was asked for Alberta address when I applied for Alberta Health Card.
Btw, Which province/state address are you giving at the port of entry for receiving your PR Cards? If you are giving Toronto/Ontario address then you can probably apply for health card in Ontario but ideally speaking, It's better to apply for health cards in Alberta to avoid unanticipated events in the future.
I guess other friends might have different thougths and experiences.
Guys quick question:
1. I am planning to complete my landing formality by road via buffalo. If I rent a car do I need to get some kind of insurance proof or anthing particular for canadian customs and border protection.
2. Also I was thinking may be staying for few days so is it possible if I can apply for Helath card in toronto itself.... any thoughts