You realize that a sizeable chunk of the parking you're removing is free incentive parking for transit riders, right? It's that many more cars that would end up on the bridge.
Besides, allow me to say that this is very similar to Devimco's plan for Griffintown in terms of scale. And like Devimco: a great idea, but not a chance in Hell it's ever getting done! And I mean that the nicest way possible.
You should be thinking more in terms of small additions to the current commercial space. Because any promoter with that kind of clout is bound to look elsewhere for a high rise development on that scale.