Veloscot, I've come to this thread late but here's my thoughts, I'm still trying to find the ideal solution for a touring bike I have.
STI/Ergo levers don't pull enough cable to operate normal V Brakes properly. V brakes need about 25mm of cable pull, STI/Ergos supply about 13-15mm. There are quite a few ways round this, none of them ideal, there are pros and cons for all of these. In no particular order:
Put Travel Agents on the V brakes. They double the cable pull from the lever. The V's will work but - you've got extra friction in the cable run, kinks in the cable that may fray, the brakes aren't easy to modulate ('cos they move a lot for not much lever movement) and the Travel Agent may interfere with a rack at the back.
Ditch the STI/Ergos's and use DT levers or bar ends (you can also find gadgets to mount these on the bars - Kelly Take Offs, Paul thumbshifters). You can then use V brake specific drop bar levers (they pull twice as much cable) from Dia Compe, Tektro or Cane Creek. The V's will work but you've lost your STI's and you got the modulation problem the same as above.
Use MiniV's. They normally have 85mm arms instead of 100mm. They need 85% of the cable pull and provide 85% of the mechanical advantage (MA - by and large the braking effect at the rim) of normal V's. Both of these will depend on your bike - the higher the rims are above the brake pivots the less cable pull you'll need and the less MA you get. You'll normally get good braking from these but you may not have enough clearance over a fat tyre and mudguard to use them. Also you may still not have enough cable pull and need to keep the pads adjusted very close to the rims requiring constant adjustment, no tolerance for rims out of true and no easy wheel removal.
Use Canti's. This is another topic in itself. By and large canti's need less cable pulll than V's and produce less MA. How much of each depends on what sort they are and how you set them up. There are basically 3 kinds of canti's:
High Profile ("old fashioned" or cyclo cross canti's like the Tektro 520's or 720's someone linked to). These are very tolerant of how you set them up but don't produce much MA. If these produce enough braking for you and don't get in the way of your panniers then it's a good option.
Medium Profile. Like Shimano BR-MT60's from the '80s. They are a good balance between power and set up sensitiviity. But they're hard to find now and still stick out a bit.
Low Profile. Modern canti's like Shimano R550's. Can have really good power ('cos they've got longer arms) if they're set up well but maybe not much pad movement. The trouble with low profile canti's is that MA decreases markedly as the pads move towards the rim which is inconvenient anyway but also means the brakes work less efficiently as the pads wear. If you can set them up optimally then they're good but if not then they can be poor.
Generally with canti setup the lower the straddle wire is the better but you can end up with lots of MA but not enough pad movement this way.
You need to be careful with recommendations people pass on. What works well on one bike may not work well on another. Frame geometry and build can make a big difference. Things like the brake boss distance apart, height to the rim, stay flexibility, fork flexibility, cable runs, hanger placement and pad compound can all make a big difference and just 'cos one arrangement works well for someone it wont necessarily work well for you. Unfortunately you'll need to try things out and see what works on your bike.
Lots of info in these links:
http://sheldonbrown.com/cantilever-geometry.html
http://www.circleacycles.com/cantilevers/canti-geometry.pdf
http://www.circleacycles.com/cantilevers/
