We have been on Grandeur & Celebrity Summit. Both had sliding balcony doors. Can you tell me if Radiance also has sliding doors?

YES...sliding doors it is. Just remember to pull the handle upwards to lock it, or you may get a whistle.(especially loud during a nice quiet nights rest) After a couple nights of this and then duck-taping the lower ledge, we reported it before heading to breakfast and when arrived back had noticed the position of the handle that they kindly adjusted....silly us!!