Hi, I've been just been having the same confusion as bleary after looking at renting a car for a trip to Canada.
I've just been searching the visa europe website to see if if they offer auto protection and I can't find any mention of it. I've also checked my VHI multi-trip insurance and as expected it is not covered :Third Party Liability: If You hire any form of mechanically propelled vehicle (e.g. car, motor cycle, moped or scooter), sail or powered
boat, or an airborne craft, no liability cover will apply under this Policy for material damage and You must ensure that cover for third party
injury or property damage is included with the cost of hire.
--
The only additional option is to get personal liability and personal effects, but these are just for if something happens to the driver or one of the passengers or possesions. There's no options for SLI or any other mention of insurance for damage to a third party.
Why do they make it so difficult? is this just a trick where they show you a good rate online, let you book it and then hit you for the SLI when you get to counter ? if you want to get cancel at that stage it's going to cost you the E45 cancellation fee.