If you missed the San-Diego Comic Con, don't worry! One user from the website Reddit uploaded almost every single image from the Korra panel, and, boy, this is really big news.
Go here to see almost everything from the Comic-Con in really high quality, but trust me, there is a lot. And I mean a lot. Your body won't be ready, trust me. Book 2 is also called "Spirits," and there will be some new characters, such as Unalok, Tonraq's brother. Bumi and Kya also play a big role. Korra, Mako, Bolin, Asami, and Tenzin have an updated look, so be sure to check that out.
By the way... they were selling these posters at the Comic-Con, and yes, it's canon. Go ahead, you can scream.