As statements they mean the same thing. The second one would not likely be used as a question. It would be more common to say "Isn't is a beautiful day?"

'Such a beautiful day' is a statement. 'What a beautiful day' could be both a statement or question depending on the tone of your voice or if its in text, then a '?' or a '!' can indicate your meaning.

The first one is a statement. The second one can be a statement or question.