I am new to cyclocross and I recently purchased a new cyclocross bike. I am having a really hard time centering my cantilever breaks. I have tried tightening both the cross-cable and the cable that runs to the hand grip. Both sides of the brake were set to the middle setting when I got the bike, but the drive side pad was contacting the wheel. I set the drive side to the highest tension setting and that centered the breaks at first, but after squeezing the grip the left side pad would not return to its starting position.

Could it possibly be that the springs on each side have a different recoil strength, or is there something more simple that I am just totally missing?

First I would remove the brake from the boss, set the spring in place, and then push the brake in towards the wheel, and let go, and see if it releases or not... if it doesn't it could be several things:
1) Brake is too tight on the boss and is being compressed to the end..
2) Excess paint on the boss, not allowing the brake to return
3) Spring
Ive experienced your problem and it was #2 for me... sand paper on the boss fixed it in a matter of seconds..

If this is not the problem look into a new stradle carrier with a screw on at least one side to hold the stradle cable in place.. most of the newer carriers have a screw on either side to lock the carrier cable in the middle...

http://cyclocrossworld.stores.yahoo.net/emstca1.html