I had a discectomy with fusion in my neck at C4/C5 in Dec. 2006 and I was able to paddle some easy class IV in late summer 2007. Our surgeries were probably quite a bit different but you could probably plan on that being the worst case (about 7 months?) unless your healing doesn't progress well. Your Dr. will tell you when it is OK to go do something dangerous, hehe.
I'm impressed that you are feeling fine after 4 weeks. Maybe it's the drugs?
I'll bet that if you hit the gym, do all of your PT, and eat right then you'll be back in no time. It sounds like you want it and that is probably most of the battle.
As for pain... from my experience I would guess that after a day of paddling you'll be on the floor on your back... but it will be worth it. My neck hurts like shit after a full day of fun but it goes away as soon as I can lounge for about 30 minutes.