NOTE: This spoiler was submitted by Jeremy.
The movie opens with Fred O'Hare (James Marsden) explaining the history of the Easter Bunnies, and how he would eventually become the first human Easter Bunny, but he'll get to that later.
Switch to Easter Island, where a young E.B. is playing on some drums before his dad (Hugh Laurie) comes to ask him if he'd like to join him at work, and E.B. is excited. He takes him down to the candy factory where everything is made, from the chocolate bunnies to the marshmallow chicks. E.B. starts sneaking some marshmallows until he is caught by Carlos (Hank Azaria), Dad's second in command. He reprimands E.B. for taking the candy but Dad covers him and says he was taste testing the candy. E.B. says it's good, but Dad says it's not, which makes Carlos pretty annoyed.
That night, the Easter Bunnies go down to a quiet suburban neighborhood on a sleigh steered by chicks to deliver Easter treats to the kids. We see a young Fred sleeping and waking up when he hears and sees the sleigh. He runs out to catch a glimpse of the bunnies but misses them. He just finds a nicely wrapped chocolate bunny on his doorstep.
About 20 years later, Fred is eating dinner with his family. His dad (Gary Cole) is proud of their snotty adopted daughter Alex but disappointed with Fred for not being able to hold a job. Everybody, including Fred's mom (Elizabeth Perkins) and sister Sam (Kaley Cuoco), starts reading off statements of concern for him, but he won't listen and leaves. Outside, Sam tells him that she has set up an interview for him at a video game company, and even though he really doesn't wanna go, he agrees to go, as well as house sit for a rich client (I think) of Sam's, but she warns him not to go upstairs.
Meanwhile, back on Easter Island, a grown up E.B. (Russell Brand) is rocking out on the drums until his dad comes up to notify him that he is about to become the new Easter Bunny. He doesn't want to do it and instead tells him of his dream to drum in a band, which Dad dismisses. Upset, E.B. sneaks out that night and hops into a portal to take him to Hollywood.
When he makes it there, he sets off to find a place where bunnies can make it, but he winds up at the Playboy Mansion with the wrong idea. He walks away disappointed but starts to convince himself to keep going for it...and then gets hit by Fred's car. Fred thinks he's killed the little guy, so he tries to smash him with a rock until E.B. wakes up tells him to stop. Fred freaks out and runs into the house he's supposed to take care of, and E.B. follows. They make a compromise and Fred lets E.B. stay in the garage.
Back on Easter Island, E.B.'s Dad notices that his son is gone, so he assembles the Pink Berets, three cute but malicious bunnies that go through the portal to retrieve E.B.
The next morning, Fred is headed for his interview, but notices E.B. is not in the garage. He finds him UPSTAIRS playing Rock Band and having flooded the jacuzzi. Annoyed, Fred puts him in a box and drives off to abandon him. E.B. tries to talk him out of this, so he says he's "special" and tries to prove this by pooping jellybeans on the hood of his car. Still not convinced, Fred is prepared to leave until E.B. tells him the children won't get their Easter baskets. Fred then realizes that E.B. is the Easter Bunny and lets him come along.
Fred leaves E.B. in the car for the interview, but he gets out when he spots the Pink Berets. Fred meets with the interviewer (Chelsea Handler) and does not make a particularly great impression (he lies about being a writer and fudges the plot of his "novel" by using the plot of Avatar, which the lady catches).
In the building, E.B. comes across a group of blind singers and plays the drums splendidly for their absent player. One of them gives him a pamphlet to meet with David Hasselhoff to perform for his talent show.
Later, Fred is visited by Sam and tells her the interview was a flop. She tries to comfort him but hears something from upstairs and finds E.B. posing as a stuffed toy. She thinks he's cute and then reminds Fred to go to Alex's play, which he does not want to see, but goes anyway.
Back home on the island, Carlos, finally fed up with being looked down upon, plots a revolt with the other chicks to take down the bunnies.
Fred takes E.B. to Hoff's show and plays the drums so well that Hoff allows him to perform on his show. They then go to Alex's show, which sucks because she cannot sing (despite bragging earlier that the teacher loved her voice). Thinking he spots the Pink Berets, E.B. Runs onstage and ruins Alex's moment, but E.B. covers them both and acts as a ventriloquist dummy and gets everybody to sing "I Want Candy." After the show, Fred's dad continues to ask when he'll stop slacking, but as Fred sees the kids in costumes, he gets an idea.
At home, he tells E.B. of his idea to become the Easter Bunny, so he can go be famous. He thinks it's a crazy idea at first, but lets Fred go through with it. A montage follows with E.B. training Fred to do the Easter Bunny job, cutting between Carlos trying to shape up for his own big moment.
The next day, E.B. prepares to go off to Hoff's show, but notices that the Pink Berets have found his location. He fakes his death by putting his clothes on a stuffed turkey and boiling it. The Pink Berets find the turkey and Fred. Thinking he killed E.B., they shoot sleeping darts at him and capture him. They take him to Easter Island, and he is amazed by the factory. He thinks he's getting a warm welcome at first, but they present the turkey (clothes still on) to E.B.'s dad and accuse Fred of killing E.B. This gives Carlos the perfect opportunity...he tells the bunnies there will be a service for E.B. in the chamber, but he locks them in there and reveals his plan to the Easter Bunny. He ties him and Fred together.
E.B. starts feeling guilty about ditching Fred, so Hoff lets him go back to him, but he is too late and finds the dart in the floor. He knows what's happened, so he heads back home and discovers the chicks have taken over. Fred and E.B.'s dad are hanging over a boiling pot of...baked beans, I think it was...but the two escape after Fred discovers they are tied up with black licorice (which the Easter Bunny thinks is horrible). E.B., after narrowly escaping his own death, goes to stop Carlos and the chicks from taking off in the sleigh. While holding the Egg of Destiny (a scepter that only an Easter Bunny can hold), Carlos transforms into a weird half-chick/half-bunny hybrid. As they are taking off, E.B. distracts Phil (Carlos's own second banana) from leading the other chicks by playing a beat on the drums. The chicks feel the beat and the sleigh goes down.
With Easter saved, E.B.'s dad forgives him for being selfish and dubs him and Fred co-Easter Bunnies. Back in California, Fred shows his family that he has finally done something with his life as E.B. comes in on the Easter sleigh. Although they find this to be really weird, the whole family, even Dad, are proud of Fred. He sets off with E.B. to deliver baskets, and it is revealed that Carlos (still half-bunny) and Phil both get to stick around, but as the two leading chicks of the sleigh.