How do you get the electricity back in sunny shore?After that what do you do?
You have to go to the Distortion world and beat Cyrus also catch/beat Giratina. Then you will restore power and gain access to Sunyshore city.
It's in sunnyshore city but you need to kill,catch or run from giratina in distortion world. When you have done that go back where sunnyshore is. Then go up the stairs that are outside and look everywhere that is upstairs and you will find the gym place.