Good news: Vancouver is the car-sharing leader of North America, with the most vehicles per capita. The principal car-sharing services in Vancouver are
This is the most widely used service; cars are usually conveniently available when you want one. Rentals are point-to-point — you can drop it off anywhere in the home area (basically within Vancouver city limits). However, since Victoria is outside the zone, you would be looking at full-day rentals for the duration of your Victoria excursion (~ $100/day).
Nearly all Car2go vehicles are two-seater Smart cars — possibly insufficient for your luggage. There are a few four-seater Mercedes vehicles, at a higher price, but you would have to be extremely lucky to find one near you, especially if you need one at the airport.
This is a newer service, with similar pricing as Car2go, but you get a Toyota Prius.
This is a local car-sharing operator, with presence in Vancouver, Victoria, and Nanaimo. modo rentals need to be pre-booked, and you must return the car to the original location before the agreed-upon time.
A major global car-sharing operator, with a relatively small presence in Vancouver and Victoria — mainly downtown.
The decision depends mainly on how long you actually need a car.
Public transportation in Vancouver is quite good. (I'm less familiar with Victoria.) You could supplement public transportation with car-sharing as needed.
You could just rent a car for two weeks from a traditional car-rental company. That could be cheaper than paying the maximum daily rate every day for any car-sharing service, even after considering taxes, airport fees, fuel, insurance, and parking.
One thing to keep in mind is that taking the car on the ferry is not cheap: you would be looking at an additional ~ $100 round-trip to bring the car. During the summer weekends, if you are travelling with a car, I would strongly advise you to make a reservation as well — an extra $20 or more. Therefore, if your luggage is light, you may wish to consider taking the 620 bus to Tsawwassen Terminal and renting a car on the island.