There are basically two forms of liability coverage that you might need and I think both are pretty important for a photographer. First, you will want to have some of what is called business liability coverage or office liability. This covers bodily injury and property damage mostly and an example of how it could be useful is if you leave a piece of equipment on the floor and a client trips on it, injuring themselves. Many companies offer this and you would probably be best off checking with an independent agent who works a lot with businesses. Usually it will come in a package that will cover your equipment for theft or accidental damage as well, kind of like how a homeowner's policy works for your personal liability and belongings.
The other sort of liability coverage is called professional liability and it covers damages due to your performance of your job. For example if a client sues you after you shoot their wedding because they think that you did a lousy job. This coverage is included in normal PPA membership, but I don't know about Canada for that. I think it might be harder to find folks who offer this coverage, here in the US, State Farm will cover a photographer with a business/office policy, but not professional liability, for example. I do think that the afore mentioned independent agent who does a lot of business coverage is your best bet here if you can't get covered under PPA. If you are eligible for the PPA coverage, I think it is a fantastic deal.
In a former life I was an insurance agent, by the way.