Having had v-brakes with Travel Agents (linked to Campag Ergopower 8 sp) on my tandem, my conclusion has been that v-brakes are total crap (too much looseness in the system, and this is with Shimano v-brakes and Tektro mini-v-brakes), the Travel Agents remove any mechanical advantage v-brakes might give you, and brake adjustment with brifters/no Travel Agents has an extremely narrow/limited scope. I would stick with the cantis and try different pads. V-brakes were designed for mtb's in off-road conditions. They are completely inappropriate on road bikes with road levers.

btw: the tandem is currently running dual-pivot sidepulls, the best rim-brake technology so far.

Luis