Originally Posted by Six jours

CX bikes use cantis because caliper brakes tend to clog up with mud. Cantis can also be extremely effective, comparable to the very best calipers. But the stock brakes on the Motobecane Fantom CX are crap. If that was my bike at the very least I would replace the awful stock pads with something like Kool-Stop salmons. If you combine those pads with better brake geometry, like the inexpensive Tektro DR720, or the pricier Avid Shorty, then you will have nothing to complain about.

Now, if you're not worried about mud and really are set on using calipers, then you have some work to do. First, your fork is probably not set up for modern recessed calipers. This means you have to use a caliper designed for the older, external nut style. Most modern nutted brakes are pure crap and almost completely useless. You can find good quality vintage nutted brakes, but you kind of have to know exactly what you need.

Beyond that, long reach may not be long enough. It looks to me like that fork might be on the border. If you need extra long then you are truly hosed. I have used a variety of extra-long reach brakes and have never found any that weren't awful. Extra long reach arms are so flexible that you get chatter, squeal, bottomed-out levers... pretty much the whole encyclopedia of braking problems.

Short version: you're heading down a road with a long learning curve and an almost certainly unpleasant outcome. Smart money is on either upgrading your cantis and pads, or replacing your fork.