In the last episode of Arrow (named Left Behind), we have already seen that Laurel steals the vigilante clothes of her late sister and debuts herself as the new Canary.
And we saw Ollie getting picked up by Maseo (disregarding all the theories of Lazarus Pit, sorry fans). And later nursed back to health by Katana (aka Tatsu).
Now the question is, will Katie Cassidy be able to perform as better as Caity Lotz or not. We have already seen how badass, the old canary is, and she has kicked some real ass. She also trained Felicity, due to which she was able escape her old Gothic boyfriend. On another note the synopsis for the 13th episode of Arrow - "Canaries" has been released as below:
VERTIGO (GUEST STAR PETER STORMARE) RETURNS AND PITS CANARY AGAINST BLACK CANARY - Oliver (Stephen Amell) is thrown by the changes within Team Arrow. He's used to calling the shots but sees that the team has evolved in his absence and tensions quickly escalate in the lair. Oliver is furious that Laurel (Katie Cassidy) has been going out as the Black Canary and tells her to stop risking her life, but when Vertigo (guest star Peter Stormare) hits the streets again, Laurel goes against Oliver's wishes and tracks down Vertigo who hits her with a full dose of the drug. Laurel's biggest fears revolve around her sister Sara (guest star Caity Lotz) so the Vertigo causes her to hallucinate an epic fight between Canary and Black Canary. Meanwhile, Chase (guest star Austin Butler) surprises Thea (Willa Holland), and Roy (Colton Haynes) warns Thea to stay away from Malcolm (John Barrowman).
If you read the above spoiler, you know that not only we get to see the cat-fight between the two Canaries but also Ollie's return and his reaction about the Canary's debut as a vigilante.