LarDasse74 has probably hit the nail on the head. I have found that with cati brakes, the strength is often determined by the length of the straddle cable. To maximise mechanical advantage of a cati brake system it is normally better to have a shorter straddle cable. This will make the brake setup look like an equilateral triangle. Another VERY important point is to attach the brake pads properly. The brake arm face should be parallel to the rim when the brake is fully applied. With peg type brakepads it can be tricky to set up. Many people back the pad up to the brake arm face, which is normally incorrect. With bolt on pads, rearranging the spacers will do the trick. On my touring bike I have the canti brakes set up so that they are really strong, but the straddle cable is too tight to disengage when removing the wheel, I need to loosen the whole brake cable.
Also, someone else on this thread suggested changing the brake pads. This has worked for me in the past.
I think if you change the whole brake system with v brakes then you will be throwing away time and money. Once canti brakes are properly set up, they are far better than v brakes.