Isn't the cost of renting an RV dramatically different by country/city? For high-end cars I've found 100%+ difference in cost, in which case this might be far more important than the cost of airfare. At Geneva, for example, I often rent cars from the French side instead of the Swiss side due to the cost being 30% lower (same airport, just exit in a different country, and a few km drive to get back into Switzerland).

I'd focus on locating the RV that you want to rent, and then figure out how to get there from YYZ