Sara Lance has had a long-running history in Starling City on Arrow, and spent most of her time during the past few seasons as Black Canary, defining the role for DC on TV. So while she's not necessarily a new player when it comes to the heroics of a vigilante, her return to the show marks her debut as White Canary, an obvious contrast to her previous vigilante persona.
In a recent interview with E! Online, the show's executive producer Mark Guggenheim elaborated on when fans can expect the change, and part of the reason why her return is so important:
"The White Canary will be launched in the first few episodes of Arrow ... 4x08, our typical crossover episode, will be doing a lot of heavy-lifting in terms of getting the Legends of Tomorrow characters set up and also seeing where they are with relation to The Flash. It’s a big episode.
So far, WB has knocked it out of the park with managing the often gigantic casts of their crossover episodes, and establishing ongoing relationships that connect their shows in unique, but (more importantly) coherent ways. Their plans for White Canary are unclear, but with her set-up promised within the first few episodes of Arrow's fourth season, fans won't have to wait too long to see what happened after Sara allegedly died at the end of Arrow's Season 3 premiere.
In tune with a lot of the shifting aspects of storyline within their TV universe, DC seems to be keeping this incarnation of White Canary completely separate from her comic book counterpart.
The comic version of White Canary is the Black Canary's arch nemesis, a martial arts master named Si Fu Huang, and was created by Gail Simone for this past year's run of Birds of Prey. Very obviously, Sara Lance's path may not follow Huang's, but the endless possibilities of what her role in the Legends of Tomorrow will be is more than exciting enough to keep this fan speculating.
Season 4 of Arrow premieres on October 7th, 2015. DC's Legends of Tomorrow premieres in 2016.