Question is if you lose consciousness before the pain hits
Also where it hits you. If it swims through your leg I fear you will feel it for some time.
Now if it hits you square in the chest, lights out.
Being hard and small, the tuna can can produce much more localised and sharp pain. If the whole tuna is dropped on your lower body from the third floor and turns it into mush it would also hurt though. But I still vote for tuna can.
A dropped 500g can of tuna from the third floor aimed at your lower body will hurt less than 250kg of tuna dropped from the same height.
Most definitely, but a can of tuna shot by a tuna can cannon? The argument does not specify similar circumstances!