Someone correct me, but Sora road levers have more leverage (mechanical advantage), while with canti brakes it's the brakes with more leverage. So it's really a question of getting Sora brifters working with the CR720 rather than something "inherent" with Sora brifters.

I think, and this is where I could be pulling from nether regions, that the trick would be getting the pads as close as possible to the rim so that the longer pull from the brifters can apply enough pressure. Get the wheels as true as possible and pull the straddle cable in as far as possible.

Or find some sort of "travel agent" to change the pull ratio. Which someone here should know something about (I don't).