Because you indicated you occasionally have non-family members as passengers in your car, we recommend Additional Third Party Liability for you. The more passengers you have in your car, the more damages you can be liable for in the event of an accident – not only are non-family members not covered by most standard insurance, they are also more likely to file law suits.
For example, if there's a ticket you forgot to include, or you decide to go with a different deductible, then your auto insurance rate will likely change. The same is true too, if you choose not to bundle your home insurance but originally indicated it was something you'd consider doing. If you don't end up getting home insurance with the provider you buy your auto insurance from, then you'll lose the multi-line discount that was originally applied to your auto insurance quote.
Another important aspect of buying car insurance at a rental location – it probably has much lower insurance limits than your personal car insurance. Let’s say, if you have $2,000,000 liability on your personal policy, an insurance policy purchased in a rental location might only have the minimum required by law – and that’s just $200,000 in Ontario.
This insurance is required by law throughout Canada. It covers the costs associated with damages caused to another person or vehicle in an accident, including medical bills, rehabilitation, lost earnings, legal fees, and other expenses up to the limit of your policy. As a practical matter, you'll want enough insurance to cover a judgment against you in a major accident so that your personal assets won't be put at risk.
As for best place to shop for insurance, I always try Kanetix before I buy any car (new or used), and every year before my insurance is up for renewal. For the past 4 years TD has been the cheapest for me, but that doesn't mean it'll be cheaper for everyone. It depends on how many cars/drivers you insure, if you insure property, and of course it depends on your record, experience, etc.
Keep in mind that the minimum car insurance coverage required is determined by the Government of Ontario and may vary in comparison to Alberta, New Brunswick, Newfoundland/Labrador, Nova Scotia, Prince Edward Island, and Quebec. In addition, premiums can vary depending on the area in which you reside, typically being higher in major urban centres, such as Toronto.