There's no pronounciation difference. Both are grammatically correct, but the former is a nominal phrase (э́та интере́сная кни́га 'this interesting book') and the latter is a complete sentence (Э́то интере́сная кни́га 'It [is an] interesting book').
«Эта книга интересная» is "This book is interesting".
«Это книга интересная» is basically «Это интересная книга» with an inverted word order. This could be used for contrast (Это кни́га интере́сная, а то — ску́чная. 'This is an interesting book, and that is a boring one.'; since интере́ская is contrasted, we put it at the end), for example, but in most contexts this doesn't really work.
For the difference between э́то/э́та, see guide by Olimo: https://www.duolingo.com/comment/11536858 Note the difference only exists in writing, but not in speech (э́то and э́та are pronounced in the same way).
That would be «эта интересная книга» (note the feminine form «эта» instead of the neuter «это»: neuter is used for a self-standing pronoun, but if you want a pronoun qualifying книга, if should agree with книга’s gender).