This is true, but I feel that changing Carl's gender would change Ellie's identity and gender, as for the plot to work, it has to be the deceased person who truly craved adventure, and. . .that works so well with Ellie, and she's such an amazing character, dead or alive, and so is Carl .. .and I wouldn't want to change their story.

Russell, yes. Russell could easily be female. The dog thing, though. . .well, if Dug was female, the others would be, as the Pack is set up to be bullies, and cross-gender bullying is rather rare in media.

At least we got a non-white Pixar main character in Russell?