Katie Cassidy and Juliana Harkavy Invite Margot Robbie to Join 'Green Arrow and the Canaries' (Exclusive)

The 'Arrow' actresses are spilling exclusively to ET about their potential spinoff and why they'd love a 'Birds of Prey' DC crossover!

Step aside, fellas -- it's time for the ladies of Star City to take control!

On tonight's penultimate episode of Arrow -- appropriately titled "Green Arrow and the Canaries," -- fans are getting a special sneak peek at what life after Oliver Queen's (Stephen Amell) death looks like in Star City in the year 2040. This standalone episode, which is known as a backdoor pilot, will serve as the start of a potential spinoff series coming to The CW.

This one-hour episode features Katherine McNamara suiting up as Mia Queen/Green Arrow, while Katie Cassidy is back kicking butt as Laurel Lance/Black Canary and Juliana Harkavy is reprising her canary cry as Dinah Drake/Black Canary.

ET recently welcomed Cassidy and Harkavy into our studios (with an exclusive surprise appearance from McNamara!) to get the inside scoop on this action-packed episode, their hopes for this potential series' future and why they're extending a special crossover invite to Birds of Prey star Margot Robbie!

"It was amazing!" Cassidy gushed when asked about filming this female-centric super series. "What's nice about it is it feels fresh but it still has the same esthetic and it still lives in the same world. The episode, the show -- it just takes it to another level. It elevates things in a way and it was fun, especially for our characters and what they've gone through to get to this point."

"Just women kicking a** and a lot of action -- and it's definitely a time for that. It's incredible and I love it," Cassidy added with a smile.

The CW

"We just honestly felt so grateful," Harkavy explained. "We'd been so overwhelmed with gratitude to have this opportunity. This possibility of a continuation of this world exists and it's women and it's us and our family and we get to star together, so we're just so happy and excited."

One of the things we at ET were excited about was surprising Cassidy and Harkavy with a special "fan question" courtesy of their MIA co-star. (Pun totally intended!) McNamara was not able to join our interview in Los Angeles as she is currently filming another project, but she did send in a video asking her Canary co-stars to reveal their favorite part of filming this episode.

"I think the moments when we were all together in costume after we had accomplished our things -- I'm not going to give anything away," Harkavy teased. "But we were just together, as a group, as a team and just feeling that energy of all of us together and our power and knowing that we have this whole future ahead of us."

Speaking of the future, there's one DC Comics crossover that Harkavy and Cassidy would absolutely love to make happen: Bringing any of the big-screen Birds of Prey stars on for an episode!

Warner Bros.

"All of the actors [and] Margot Robbie, you are invited to come into our show," Cassidy proclaimed. "If you want to come and maybe do a little cameo, we would totally be fine with that."

"Oh, please!" Harkavy immediately echoed. "Yes, please! Any of those girls. That would be so fun!"

Harkavy continued, "It's a cool thing that [both of these projects] are happening at the same time because one of the themes of our show and the way that we interpret the comic book story is that -- especially with our characters -- there can be more than one Canary. It's not about there is one Black Canary. It's like, any woman can be the Black Canary. It's about [heart] and it's about your integrity and it's about your inner strength. So I think it's kind of cool because it kind of sets that standard on a bigger level with our characters."

This wouldn't be the first time that the DCEU movie characters have crossed over with the DC Comics TV shows! Last week, the internet exploded when Ezra Miller's iteration of the Scarlet Speedster came face-to-face with Grant Gustin's The Flash on The CW's epic "Crisis of Infinite Earths" conclusion.

Don't miss the special Arrow episode, "Green Arrow and the Canaries," when it airs Tuesday, Jan 21 at 8 p.m. EST/PST on The CW.