I really like the answer given by Calvin. It appears to be a matter of how you position your body when driving and kayaking. While I am not an expert at kayaking, both activities seem to invite the upper traps to get involved. Those muscles are already easily incited at best of times, and I would venture that faulty movement patterns over time have caused this chronic problem.
I would also predict that you are likely to get the upper traps involved in other tasks of daily life such as using a computer.
You will need an assessment from somebody who can look at you to help you determine the best sequence to relieve the pain. Be prepared for a lengthy process. Correcting faulty movement is rather difficult because you have to re-program old habits, and those are notoriously tricky to change.
I wish you good luck and hope that you will find a path out of pain.