I sympathize with your feelings. I don’t understand why people would think that frou-frou dogs (especially poodles) are always female. That doesn’t make any sense.
I’m a cat owner, but I totally understand what you’re saying. My family has two Persian cats (one of each sex, but they’re neutered) and my male cat sometimes gets assumed to be a girl because he’s got long, silky fur which is more pronounced in him than in my female cat. And one of my friends has a female bulldog named Clementine, and she says that her dog is called a “he” despite the obviously feminine name.
Dogs other than frou-frou dogs are usually assumed to be male. It doesn’t help that some little kids think that all dogs (besides poodles) are male and that all cats are female. In fact, that’s how cats and dogs are usually portayed as in fiction. You hardly ever see movies with male poodles. (An exception: calico cats are almost always female because it’s related to sex chromosomes.)