Cantilever brake set up

you see where the spring tension adjust screws push on the end of the springs? try and unhook the spring from there and physically bend it to increase the tension on one side (the side that's rubbing).
This is what worked in the end. I took the cantilever body off the boss, left the spring attached to one of the tension holes, and pushed down a bit on the bit that attaches to the body. The main cable is now pretty much vertical. Cheers,