Book, Dark Disciple.
Here's a link to an article about some untold stories: http://www.ign.com/articles/2015/04/17/star-wars-the-clone-wars-tons-of-info-and-images-from-the-unfinished-episodes
Here's a link to an article about everything intended for Ahsoka:http://io9.gizmodo.com/the-untold-stories-of-ahsoka-tano-broke-our-hearts-and-1783725803
Also there is a comic that resolves the cliffhanger in Darth Maul's storyline titled "Darth Maul: Son of Dathomir". The comic itself hasn't been reprinted for some reason so it's extremely expensive but you can definitely find somewhere to read it online.
Plus a novel that continues the story of Asajj Ventress titled "Dark Disciple". It's a solid book and well worth reading IMO. Here's an Amazon link to purchase if you're interested: https://www.amazon.com/Dark-Disciple-Star-Christie-Golden/dp/1101884959/ref=sr_1_1?s=books&ie=UTF8&qid=1473034349&sr=1-1&keywords=dark+disciple
Read Dark Disciple, it IS considered canon.