It's known that Arrow Season 3 is building toward Laurel Lance (played by Katie Cassidy) becoming the Black Canary, and now it has become known just when that will happen.
Last night saw an advanced screening of The Flash Vs. Arrow crossover where - slight spoiler - it's learned Laurel will not play a large role in the two episodes. The good news is there is a specific reason why.
Arrow Season 3 EP Andrew Kreisberg filled in the details to THR.
"Laurel appears in the Arrow episode. She's not as present in these episodes, but that is because we've been building up to her appearance as the Black Canary. We sort of said that Sara was the Canary, but Laurel is the Black Canary. Episodes 10, 11 and 12 are a three-part trilogy that are about her. And episode 13 I think I can spoil, is called 'Canaries.' For fans of Laurel and for fans of Katie [Cassidy], they're going to get more than their fill after the winter break."
Speaking of Sara, it is also learned we will find out who her killer is in Arrow Season 3 (via EW.com):
I took your question straight to executive producer Marc Guggenheim: “I’ve always maintained that you’d find out the answer to who murdered Sara by the end of the year,” he says. “That said, I will say that the S.T.A.R. Labs team is going to end up providing a critical piece of information that cracks open the whole case, but that doesn’t necessarily happen in [the crossover].”
"Arrow" airs Wednesdays at 8pm ET on the CW.