to get past the guy blocking the way to sunyshore. you go to mt.cornet and you surf across the water and use rock climb.then there is a cave that go threw. and then theres place that's snowing.
go to the top of mt. coronet, make sure you have at least 10 max repels to get through fast, and battle the team galactic bosses. capture dialga and go back inside the mountain, find the nearest...
beat snowpoint city gym then get palkia if you have Pokemon pearl or go and get dialga if you have Pokemon dimond then try again then you should be able to get there.