It depends. Some consider them canon if they fit seamlessly into the established Samurai Jack universe and don't contradict the main storylines. Others might have different opinions.
It depends. Different people and franchises might have different criteria for what constitutes canon. Sometimes it's clearly defined, other times it's more ambiguous.
Anime canon refers to the content that is considered official and part of the anime's storyline. Manga canon is the content that is officially part of the manga's story. Usually, anime canon is based on manga canon but can have some adaptations or additions.
One great Samurai Jack female Jack fanfiction could be 'The Adventures of Female Jack'. It might show her facing different challenges in the same post - apocalyptic world as the original Jack. Another could be 'Female Jack: A New Path' which could explore her forging her own unique destiny, different from the male Jack's journey.
Anime canon might have some changes in visuals or pacing. Sometimes, scenes are reordered or added for better animation flow, but the core story usually remains similar to manga canon.
The main difference is that sometimes the anime might add or omit some details to fit the animation format or time constraints. But the core story and characters usually remain the same.