OK, but do you think I should just install the new canister, or have Toyota do the fix as well?
If it were me, I’d just do the new canister. It sounds likely that your problem was caused by routinely overfilling the gas tank, since you said you’ve 'fessed up to doing that for years.
Even if the problem was caused by the water intrusion problem, which I doubt, the car still went 5 years with the original design before the problem surfaced, so you should get another 5 years out of the new canister without doing the water intrusion fix. But I bet you will get more years out of it just by not overfilling the tank.
I have mixed feelings . . . and I’ll explain why
In cases where there is a bulletin, which involves an evap repair and modification, I’ve found that if you only address the symptom . . . the canister, in this case . . . without addressing the root cause, it usually comes back to bite you in the butt. Until you bite the bullet and do the modification.