Im pretty sure this one is ASB. Both the germans and the Japanese came up with proposals to hit the canal. Adolf Gallhand taking a flight of Fw200 condors on a on a one way ticket out to the canal , before ditching in the sea for the remote possibility of a U-boat pickup. I think the Japanese wanted to send some submarines or small naval task force. Both nations decided against these schemes for good reasons , they would both be suicide missions. The US had a large amount of forces in the area , including a naval task force and land based aircraft.
Even with a full out strike, there is not much that one can actually do to dissable the canal. The lock gates on the Ocean ends (the most accessiable points) would have been very difficult to hit from the air , and due to the sheer size and sturdyness of their construction , even direct hits by large ordinance would have been unlikely to have put them out of order for any period of time. Even if they did , the might of the American industrial machine could probably have seen them repaired or replaced in a matter of weeks. The only way i can see the canal being disable on a long term basis are:
1) The ramming of a explosive filled ship into the outermost lockgates (ala, the HMS campletown during the Nazaire raid ,
http://en.wikipedia.org/wiki/St._Nazaire_Raid )might have done enougth damage to the lock itself to have neccesitated rebuilding the whole thing , or damaging the inner gate enougth to allow a unbalenced water level.
2) Destroying the Dams that held back Gatun lake would effectively drain the centre part of the canal , and cause a massice tidal wave that would surely destroy much of the local infrastructure. However , as these targets would have been impossible to hit from the air or sea , it would have require a large scale commando raid , somthing that would not likely have succeded.
Nice try though , i had to think about it