Instead of blowing up the lock why not just block it. Fill the hold and lower decks with quick drying cement, you can scuttle the vessel in a lock. Rig a couple of floating shape charges for quick detonation and use them to damage the gates, further delaying any salvage attempt. The concrete would not be an unusual cargo if boarded and it would take much longer and effort to re-open the blockage.
Also consider that the Chi Coms, who have a very heavy financial investment in the canal, are going to be very upset at you as well as the US.

B.