"I'm getting married, Doctor Strange is at the wedding," McAdams told ET's Will Marfuggi during the Multiverse of Madness junket, sharing where her character finds herself at the start of the film. "It's still complicated with us. We still haven't quite found our groove, but we're still dancing between friendship and love and where does it all end up?"
While Christine was left somewhat in the dark about most of the first film's magical revelations, she gets to play a more integral part in the sequel, with McAdams stepping into the multiverse herself.
"I play a little bit of a different character in the multiverse," she shared. "She's a lot more used to the strangeness of the MCU Universe, so she's not as fazed by it as emergency room Christine Palmer."
"We've been opened up to endless possibilities, to multiple universes, where characters present themselves as entirely different people," the actress added of how the opening of the multiverse affects the new film. "People you think you recognize, but they're completely opposite. They're good, they're sinister... endless possibilities."
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Benedict Cumberbatch on Future of 'Doctor Strange' After 'Multiverse of Madness' (Exclusive)
However, McAdams added, some things about her character remain the same no matter what universe she's in.
"I think it's very much in her wheelhouse to just kind of roll up her sleeves and dig in," the actress said of her character. "No matter how strange or foreign or unbelievable it is, she's gonna help. She'd do anything for Doctor Strange, and I think she'd do anything, as a doctor, to protect people and help them. That's her oath."
McAdams said she enjoyed returning for the sequel, reuniting with the cast and crew and getting to work alongside Cumberbatch once again.
"There's just a shorthand and a level of comfort," she noted. "You're back in it right away, and I also loved working with Sam [Raimi, who follows Scott Derrickson as the Multiverse of Madness director]. He is such a funny guy and he's just delightful."
"He's got this horror thing he's doing, but he's nothing like that in person," she added of Raimi, noting how the director contributed to the sequel's darker tone. "I had a great time with him as well."
As for surprises the film has in store, the actress said there were "many times" she was shocked or starstruck by who or what was turning up on set for top-secret scenes.
"It sort of adds up all the way through. It just keeps building on itself, and there's sort of no end to the possibilities. I'm excited to see it, because I had no idea who is in it or what's happening," she admitted.
McAdams noted that the sequel is also special to her, personally, as something she can share with her family -- in particular, her 4-year-old son.
"My son is a bit interested in, like, bad guys and good guys," she shared. "He's just started talking about bad guys in particular... and then my mom bought him a superhero cape."
"He hasn't been super into all of that, but I think it's just starting," she added with a laugh. "And then, we went to Target and he saw a Benedict doll, a Doctor Strange doll, and he's like, 'Mom, that's the guy from your work!'"
Doctor Strange in the Multiverse of Madness is in theaters now.