I wouldn't worry about cantis vs calipers as a deciding factor either way.

Cantis do have more power, but calipers with good pads have enough power to stop a road/commuting bike just fine.
Cantis have better clearance for big tires/fenders, but calipers have enough clearance for normal-sized fenders and tires.
Cantis are harder to setup, but not that hard.

Given two otherwise identical frames, I'd pick the one with calipers as a personal preference (some people might go the other way). But if the frame you want only comes with cantis, don't worry about it.