you have to have the move tutor teach it
Blastoise, Feraligatr, Swampert, Empoleon
Gyarados cannot learn the move Hydro Cannon. Hydro Cannon is a move that can only be learned by the Water type Starter Pokemon.
Some one near stark moutain will give you a hydro cannon TM.
Empoleon learns metal claw, drill peck, aqua jet, hydro pump, i think icebeam, and hydro cannon. best movesare drill peck, hydro pump, and hydro cannon(hydro cannon makes you recharge though)
go to a person near stark mountain
hydro cannon
if you have empoleon go to route 228 you will see a old man he teaches hydro cannon but your empoleon has to really trust you.
it does not learn hydro cannon you have to get the tm hydro cannon
Lugia does not learn hydro cannon nor can learn hydro cannon.
Pokemon learn moves at there time. Empoleon learns Hydro Pump at level 59 because it can!! Because every time you evolve3 a Pokemon its stats get better but the learning of a new move takes longer. So, for example, if you had stopped the evolution of prinplup to empoleon you could have learned hydro pump at lvl 51.
Hydro Cannon