Ryan Gosling liked both Britney Spears and Rachel McAdams for ‘Notebook’

Oh baby, baby — Britney Spears very nearly snagged the lead role in “The Notebook.” 

Casting director Matthew Barry told The Post that the 2002 nationwide search for the part of Allie — in which he saw actresses such as Jessica Biel, Claire Danes and Scarlett Johannson — ultimately came down to Rachel McAdams and Spears.

“It was tough because we did narrow it down to Rachel and Britney,” Barry said of the effort to find the perfect leading lady for the 2004 romance movie based on Nicholas Sparks’ popular novel. 

And star Ryan Gosling was impressed with Spears, Barry said: “I think Ryan would’ve preferred either of them.”

The casting director added, “the studio, for obvious reasons, would’ve liked Britney. But they also agreed and trusted [director] Nick [Cassavetes] with Rachel. That’s something that doesn’t happen anymore. A $29 million movie with two unknowns? No.”

For fans, Spears’ audition tape has become a holy grail of Hollywood. 

But now they can witness a piece of the performance she might have given. 

The day before the publication of the “…Baby One More Time” singer’s new memoir, “The Woman In Me,” in which she discusses her “Notebook” experience, Barry decided to release the coveted video — and it has spread online.

“It was time,” he said. “Taking nothing away from Rachel and her performance, Britney held her own, and it was time for her fans and everybody else to see what all the fuss was about.”

In prep for her screen test, the then 21-year-old pop star worked with Barry and his partner Nancy for two days on scenes and “getting into the spirit of Allie” before reading with Ryan Gosling, then 22, who played Noah off-camera. 

The young pair already knew each other from their early days on “The Mickey Mouse Club,” but they were all business while the tryout was going on. 

“When Britney came in, it wasn’t all hunky dory fantastic memories [for them],” Barry said. “It was very professional.” 

He added, “Ryan was very conscious of that, and he wanted Britney to have her time with Nick to talk about the role, talk about the character. And then when that was all over, it was reunion time.”

In the rawly emotional clip, Spears performs Allie’s monologue that begins, “I’m not stayin’” and leads to the actress breaking down in tears when she says, “I prayed for you to die in the war.” 

Spears wowed them. But ultimately “it was just Rachel’s role,” Barry said.

Spears writes in “The Woman in Me” that she has no regrets about losing the gig.

“Even though it would have been fun to reconnect with Ryan Gosling after our time on ‘The Mickey Mouse Club,’ I’m glad I didn’t do it,” she said.

However, 21 years after her impressive audition, Barry believes Spears, now 41, still has got what it takes to be an actress. 

“We’re all watching her with these self-made videos [on Instagram] and going ‘she’s dying to perform’,” he said. 

“Go train, because you’re really f–king good, and this video proves it.”