I don't think I understand the problem.
Is it that you can't generate enough force to close the brake, or is it that the brake is broken?
I've still got the original Tektro cantis and Shimano short reach brake-only levers on my Surly. I had v-brakes on a couple of my other bikes.
Sometimes cantis can be fussy, if the cable is too tight you may not be able to get the lever into your grip enough to put your full force on it. (kinda braking with your weaker fingertips instead of your stronger fist) If the cable is too loose you can squeeze the lever all the way into the bar and still not close the brake. My LBS came to my rescue there and put some big and juicy barrel adjusters on my brake cables so I could fuss and fiddle to my heart's content, and they adjusted the small wire that runs from canti-to-canti and then told me not to touch it... they know me so well.
Do you need new brake pads? Softer pads?
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