Car rental companies in BC are required to carry 3rd party liability insurance of $200,000. Above and beyond that, the Motor Vehicle Act provides for "vicarious liability" meaning the owner (lessor or renter) is responsible for damages, not the driver, providing it is consensual use. A recent change to the Act limits the vicarious liability to $1,000,000. What happens with a claim greater than that, I have no idea, but I think it's true that no rental company in BC offers Additional Liabilty Insurance (ALI, sometime PLI). If OP is concerned he'll have to get a specific policy from his local agent, ensuring of course that it's legal in Canada. Taxis might in fact work out cheaper.

Talk to an expert, don't rely on flyertalk (or particularly me ).

And while we're on the subject, your credit card does not cover personal liability either.