You could also try URS corporation. They have designed many moveable spans (one of their aquisitions in the 80s was Greiner, Inc.).
As for advice, I hope I am not too late, but you could ask the government for any cost data they have available. For example, the US Army Corps of Engineers builds bridges over many waterways they are responsible for maintaining. They would have cost data that you could compare against the square foot area of the deck, and give you an idea of what kind of moveable bridge options could span the gap you need to span. Since they are a public entity, they are obligated to give you any information that does not compromise national security. I would also expect the government of Canada to have similar records on moveable bridges constructed with public money.
One major item to consider is any sequence of traffic management. Most moveable bridges are two girder type support arrangements. It makes it almost impossible to manage traffic without building completely in the clear on a (nearly) parallel alignment or new alignment.
Good Luck. - Ed