How to improve front brake functionality? My front brake (cantilever brakes) does not make contact with the rim until I pull the brake levers almost all the way in, leaving me with very little space to apply extra force. That means the brakes are not working very well to slow down or stop the bike.

I'm not sure what I need to adjust -- whether it's the transverse cable or the link wire. Moreover, when I try to tighten the transverse cable, the brakes work well for a few times (or "pumps") but then suddenly revert to their original functionality. I'm not sure what's going on (if the brake cables are coming lose for example under the tension).

Any thoughts?
Thanks.
It sounds like the cable's slipping after you adjust it.  

Precisely how you adjust the cable depends on the brake design, and normally you would not shorten the straddle cable, since it needs to be a certain length for optimum operation.  However, with many newer bikes the main cable makes up half the straddle cable, with a spacer to maintain the proper straddle length.

Sheldon Brown has an article on cantilever adjustment, though it's a little short on actual adjustment operations.  Park Tool's article, on the other hand, almost goes into too much detail.