Hi Jags!
I'm a bit pressed for time at the moment, so I will give you the thumbnail sketch --
When talking v-brakes vs cantilevers, neither is necessarily "better" in terms of stopping power, but one might be better suited for a given frame and brake lever setup than the other.
Some touring frames have forks that are too narrow to take standard V-brakes
and still leave adequate clearance to function well. That can happen sometimes. Two of my drop-'bar tourers fit in this category. For them, cantilevers are a good solution that work well.
V-brakes also have different cable pull ratios, so they must be used either with v-brake compatible levers or with a gadget to change the amount of cable pull (Travel Agents are one example). If you use brifters, you'll have to use either a cable pull-adapter or perhaps choose mini-Vs or -- the preferred choice -- cantilevers. If you use v-brake levers, then bar-end shifters or downtube shifters would be the route to go. You might even wish to try something like this:
http://www.retroshift.com/ The version based on Tektro levers will work with Vs.
Depending on how they are setup, cantilevers can provide a lot of stopping power and -- again, depending on the model, the straddle carrier for the transverse cable, and the length of the transverse cable -- are highly adjustable and can be made very effective. I am happy with the cantilevers on my own touring bikes. On the other hand, when matched with appropriate brake levers, V-brakes provide smooth, progressive braking even with drop handlebars. I loved the ones on Sherpa and use the same setup in the Nomad. In each case, I could easily stop a full touring load from atop the brake hoods.
So...first choose your bike, then see what it will allow in terms of brake clearance. Once you know that, then you can go ahead and make the choices you wish for the levers and brakes you prefer.
Best,
Dan.
