Just be careful to find out which company will actually be handling the rental. The third party companies like the ones mentioned above don't have their own cars - they are simply acting as agents for the big companies (Hertz, National, Enterprise, Budget, Alamo etc.). And with the big companies, not every location offers the same quality of service since they can be run independently. For instance, the Budget at Vancouver Airport gets terrible reviews, while Budgets elsewhere get good reviews. I would want to know who is renting me the car - a cheap price isn't worth it if you get all sorts of hassles.
For insurance, check to see what you need. Sometimes the insurance cover on your own car includes rental coverage, but probably not for coming to Canada. Also some credit cards include rental insurance.
Finally make sure you price includes all the fees, like drop off, extra driver, young driver (if you are under 25) and taxes etc. And if you are using a third party site, check their offer against what the rental agency offers direct. Make sure you are actually getting a deal. And check to see if you have any discounts through other memberships like HI Hostel, automobile associations, credit cards etc.
Also, if you are from the UK, Ireland, South Africa, Australia or New Zealand, try Canadian Affair - they offer one way rental in many Canadian locations without a one way fee and get good reviews.