Christina Aguilera once claimed that she didn’t even know who Lady Gaga was. “I’m not quite sure who this person is, to be honest,” she sniffed to the LA Times 18 months ago. “I don’t know if it is a man or a woman.”

Well, she knows who she is now.

In fact, anyone who’s seen the video for her new single, “Not Myself Tonight,” might say she’s a little too aware of Gaga. An S&M latex-fest, the video features Aguilera in bondage inspired costumes, including a diamond-studded ball gag. You’d have to be blind not to see a little of Gaga’s “Bad Romance” video in it, as well as Madonna’s “Human Nature.”

The song’s menacing electronic club beats sound unlike anything Aguilera’s ever done before. If fact, it sounds a bit like a Lady Gaga song.

Aguilera, whose new record “Bionic” is out Tuesday, has been out of the spotlight for years, busy with her new son and husband. Her last record, “Back to Basics,” came out in 2006. In the meantime, Gaga has crept into the pop zeitgeist like a glitter-encrusted thief in the night.

Aguilera has certainly been thinking about where she fits in today in the current pop landscape. She’s tried on different personas and musical styles throughout her career, trying to see which one fits. Britney or Gaga? “Dirrty” girl or ’40s pin-up goddess? She obviously has never felt the need to pick just one, and she’d be the first to say she doesn’t have to.

An ominous sign that it’s not working: Aguilera canceled her upcoming summer tour on May 26, just days after tickets went on sale.

“The singer felt she needed more time to rehearse the show, and with less than a month between the album release and tour date, this wasn’t possible,” show promoter LiveNation said in a statement, also citing commitments she’d made for the upcoming film, “Burlesque.”

It was a strange move for someone with a new record to promote — her first in four years. And to music-biz insiders, the cancellation looked like an admission of weak ticket sales.

“It came about four days after initial shows went on sale to the public, which is your first indication of how the tour’s going to do,” says Gary Bongiovanni, editor of Pollstar, which covers the concert business. “She may have decided that the climate wasn’t right, the audience wasn’t properly prepared.”

Or maybe another blonde turned up and stole her career.

“It may just be that she’s not front and center in people’s minds at the moment,” Bongiovanni says. “Maybe everybody’s thinking about Lady Gaga today.”

As a single, “Not Myself Tonight” failed to crack the Top 20. And follow-up “Woohoo,” despite risque lyrics such as “All the boys think it’s cake when they taste my woohoo,” barely cracked Billboard’s Hot 100.

Aguilera’s fans are unruffled by the concert snafu: “More time to get into the album and save up my money,” wrote one on her official Web site’s messageboard. “I can save up for better seats,” posted another.

But their favorite diva seems to be having an identity crisis with this record, which Billboard derided as “cut and paste.” And the comparisons to Lady Gaga started back in 2008, when MTV News posted an item titled “Is Christina Aguilera’s New Look Totally Gaga?”

“I am a fan of Xtina,” one commenter wrote. “I will always have nothing but good things to say about her. The truth is — she so stole Gaga’s gimmick!”

Aguilera has generally kept quiet about Gaga, but while promoting the single this spring, she told an Atlanta deejay that the Gaga comparisons weren’t “even worth the breath to comment on.”

“They really are honestly two different powerhouses,” Claude Kelly, a songwriter who contributed to Aguilera’s new album, told MTV. “I also know Gaga. Once the album comes out and they hear what Christina’s doing, I don’t think the comparisons will last.”

He’s partially right — Aguilera has serious pipes, for example, while Gaga will never be mistaken for a great singer. But even that’s changed.

“Everybody knows that Christina can sing, but I’ve been telling her that she doesn’t have to blow horns off every day,” says Linda Perry, who co-wrote and produced songs on Aguilera’s last three records. “So she’s venturing out of her comfort zone and going more electronic.”

On “Bionic,” she chose an eclectic, edgy bunch of producers and songwriters, from feminist-dance rockers Le Tigre to Linda Perry to electro-rocker Peaches, as well as Santigold and Ladytron.

It might be time for her to pick a style or specialty and stick with it.

“Tonight I’m not the same girl,” she sings. All too true.