The character Showalter had to play, Ray Cutler, was a total doofus and, in my opinion, completely undeserving of the lovely, intelligent Polly Cutler (Peters). I mean. He actually "hyukked" when he laughed and who knows how much of that was character or a the actor trying awfully hard to be butcher than he was.
For instance, when Marilyn comes out of her bungalow in a hot, tight, fuschia number, Showalter says to Jean Peters, "Why don't you ever get a dress like that?" Not "because that's super hot and I'd totally rip it off you if you wore it" but "honey, you should really do something about your wardrobe." And Peters, as any best friend of the nice gay man she's married to would say, "Listen, for a dress like that, you have to start laying plans when you're about 13."
But what do I know?
Later Ray completely dismisses his wife's panic at seeing the supposedly dead Joseph Cotten in her bedroom as some silly woman thing, then pout/forces her into a business outing with the VP of Shredded Wheat and his poor yup-that's-the-bargain-I-struck wife. So, yeah, not the most sympathetic of characters.
But Niagara is a really good picture — suspenseful, beautifully shot, and worth a second look if you haven't seen it in a long time. Just think of the Cutlers as Will and Grace and it will all come out right.
I absolutely love Marilyn Monroe in this film. She's so good at that thing she does with her whole body when her character just wants more. Delicious.