Well first off it would the same amount of vehicle traffic as there is now, actually it would alleviate the traffic line ups for the ferry that exist right now.
Secondly, the ferry is the largest waste of time, its a useless boat ride. Plus a bridge would eliminate the cost of having a paid employee run a ferry that goes back an forth the length of a high school football field.
If the boatride to get you to the airport's useless, so is a car or busride. Don't you want to get to the airport? The boat is doing the job. What you have to do to justify a bridge to replace it is show why a bridge is better. A whole lot better, considering how cheap a little boat is, compared to a three or four storey high road bridge.
1) If there's no increase in traffic, the expense of building a bridge to do what's aleady being done is a total waste. Only makes sense to the degree it improves things—if you think more traffic is an 'improvement'. Porter certainly would say it is. Absolutely disagree that traffic would stay the same. It's purpose is to bet more folks onto more planes.
2) New roads don't 'alleviate traffc' they just move it to other places, and actually increase it. People drive because they can. You'll have to explain the 'existing' traffic lin-ups for a passenger ferry you walk to and from, that you say the bridge would eliminate. And while you're at it, where do the cars all go when they get to the Island. Oh Goody! New parking structures and open-air lots.
3) "A paid employee" to run the ferry? Get real, there's an entire crew, just like there'll be whole crew operating the bridge (if and when) even if you never notice them. And the bridge—just like the ferry—will need maintenence, lots of maintenence and paint and such because it's a huge structure (especially compared to a dinky-wee boat w/ a coupla diesel engines). Heck even the painter's scaffold for a bridge is a sizeable and costly thing.
4) Which brings us back to access ramps—another part of the bridge to be financed, constructed and maintained. Last proposal I saw had the cityside one as a solid wall going all the out to Queen's Quay, completely cutting off the west Harbourfront from the east. Not a nice thing to do to all those residents and other citizens just for the sake of some dozen or so passengers per plane imagining they've saved a minute or two in a couple hr. trip.
You still haven't shown any reason why a bridge would benefit anyone, except Porter and its landlord, and that only if it does what you say it wouldn't: increase traffic. Nor have you addressed the downsides we'd all be living with and paying for.
Case not made.