Personally, I wouldn't consider going from a cantilever to a long reach side pull to be an upgrade. You are trading a pretty good brake with good clearance for fenders (if you use them) for a slightly more flexible brake that is going to make life tight around the crown of the fork and around the rear tire.

I'd also be a little concerned about the fit around the cantilever brake bosses. Those are really long arms.

And for that price, you could get a set of Paul's brakes...touring or neo-retro...which is a major upgrade over just about any cantilever out there.