How do you activate you wow account after its been cancelled

If you are the one that canceled the account, then all you need to do is start paying for it again. All of your characters will still be there along with all of your gear and gold that you had before you canceled.

If you were a bad person and got caught doing something against Blizzards ToS and AUP, and they banned (canceled) your account, then you are out of luck as their decision is usually final. You can try calling Blizzard Billing, as sometimes there are mis-understandings, and try and work it out with them.