A well-known Britney Spears impersonator doesn't want to see a famous actress play the pop star on the big screen ... she says the biopic would be better served going in a different direction. Allegra DuVal, who impersonates Britney at weddings, casinos and on TV shows like FOX's "I Can See Your Voice," joined us on "The TMZ Podcast" ... and we asked her who she wants to see play Britney in the upcoming movie.