Great question — answering as the UphillTech team:
You need a Canadian Interprovincial Insurance Card, documenting that you have at least $200,000 Cdn worth of third party liability insurance (all-inclusive). The card will be in the name of the insured owner only. Just as with your standard US insurance, any driver with your permission and a valid license will also be insured while operating the vehicle.
Full answer by Jim MacKenzie: https://travel.stackexchange.com/a/110572 (CC BY-SA 3.0).
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