Are you talking about crossing the chedoke? I'd just bike to scenic drive, carry my bike up/down the stairs, then ride along longwood. I've never really been up around that area with my bike... so I'm not certain about other crossings... (I'm sure there are safe ones)
Don't try to cross the 403 proper... (quadruple railings) that's borderline retarded.
There's a pedestrian overpass if you put your streetview man (google maps) just north of the linc/chedoke 'interchange', but I'm not sure how to access that.
edit: and yes, I've done it.. not sure if its expressly forbidden but 'you cannot ride on the highway' I've heard from a number of places, people and sites, here are a few things you can be ticketed for...
click