To go back to the original issue - Brakes.
Cantis can be very sensetive to straddle cable set-up, so it may be worth considering having a play with the height/length of the straddle wire.
Also, pads can be critical. I've found that fitting longer "V" brake cartridge pads (72mm, triple compound clarkes ones from memory) transformed the cantis on my cross bike). I bought some on sale at
CRC a while back for about £2 a pair, with an additional set of pad inserts included!
Be aware that Mini-V's tend to need setting up very close to the rim to be effective.
Maybe a change in set-up or pad type is all you need, before you start throwing money at a new bike?