In the G1 series, Galvatron transforms into a Cybertronian Howitzer Cannon.

megatron is already galvatron. in transformers 2 they reserected him and in the comic books when ever megetron is brought back he becomes galvatron. they just don't reffer to him as galvatron in transformers 2

Galvatron , in an altermate universe , is the leader of the Decepticons taking the form of a laser cannon . ~ See related link below .

Galvatron uses Megatron and is Decepticons in to his and he uses Megatrons body as Galvatrons

Dalton refused to work with the Decepticons and lent his aid to the Autobots Instead of Unicron transforming Megatron into Galvatron Who reform him into Galvatron in Age of Extinction.