Like Casblanca, Some Like It Hot is a film that's literally unimaginable with different casting, without Jack Lemmon's mad-aunt drag performance, Tony Curtis' Cary Grant impression (perfected during the war, when Curtis was stuck on a submarine where the only film was Gunga Din, shown over and over again) or, of course, Marilyn Monroe. It's actually thanks to Monroe's star power that we have the perfect casting of the male leads. Before she got involved, the studio wanted bigger names - Bob Hope, Jerry Lewis, Danny Kaye or Frank Sinatra. (One has to feel sorry for any agent given the job of asking Sinatra to wear a dress.)
One oddity about Monroe's performance is that it must be the only film in which she plays a Pole - Sugar Kane is actually Kowalcyzk, as she tells us in her first dialogue scene. In fact, one of the surprising things about the film is quite how multi-ethnic it is; the gangsters are clearly Italian, the cop Mulligan is Irish (and played by the gangster film veteran Pat O'Brien), Osgood the millionaire is an east coast WASP, Poliakoff the agent is Jewish. So, possibly, is Joe, the Tony Curtis character - he certainly speaks a bit of Yiddish, referring to himself, quite accurately, as a 'no-goodnik'. (Of course, the actor who played him was Jewish, but that doesn't prove anything - the same is true of Butch Cassidy, Sonny Corleone and Harry Potter.).
This understated multi-culturalism (and yes alright, it's a very white multi-culti; there is one black character - a railway porter - but it's very easy to miss him) is one reason why it's such a verbally lively film - everyone speaks sharp, witty dialogue, but all in slightly different idioms. It's been argued that part of the film's appeal lies in its sexual inclusiveness - the belief that even two skirt-chasing no-goodniks can become better people by wearing dresses. In a similar way, it seems to suggest that vitality (that heat that some of us like) comes from a mix of national energies.
In this, we have one of the great strengths of the American film, especially in its peak talking period - roughly, the half century between The Jazz Singer and Star Wars. Hollywood was built by emigres, mostly from Eastern Europe, and gained its cultural ascendancy partly because, more than anywhere else, it epitomised the values of the melting pot. Everyone brings something different to the party, and no one ethnicity, or gender, is sufficient by itself. Like the man said, nobody's perfect.