You'll need it to have high Happiness/Friendship in order to evolve it.
Level 37.
Level 30.
level 28
Level 30.
Level 18.
Level 26
Level 25
at level 40 it should evolve into drapion
There are not trainers with a Buneary in SoulSilver.
you have to evolve it with a water stone
Donphan doesn't evolve.
Spiritomb doesn't evolve.