Probably the flavour is meaty in the dog one, whereas it's aniseedy or something for bunnies. The graduations may also be different weights on the tube so the dosing might work out different.
You can also get panacur for puppies and kittens in a liquid form, which used to be used before panacur rabbit became available. That works out loads cheaper if you have lots of bunnies but technically it shouldn't be used now there is a product specifically licensed for rabbits!