Will these fan leagues always only consist of canonical characters?
Yes, the character must have appeared in the manga or extra material in some form. I am pretty lenient with that - e.g. Migihashi, while having an anime episode dedicated to him never made it into any of the manga chapters and was only briefly shown and mentioned on a color page and in one of the pair puris - but there needs to be something for me to base the movesets on.
I could take this to greater extremes than what's currently the case by including e.g. all the American reps we have names for so far, but I'm always under the impression that it's mostly me who gets enjoyment out of something like that, so I tend to try not to overdo it.
If so, what about the girls? I know there aren't many who actually play canonically, but they are still there.
Like Hardy said, unfortunately none of them are really good enough to use. Like, the character with the lowest stats right now is Kadowaki at 10 total, but none of the girls would probably get a total of more than 3 or 4 points. If there were any girls on at least national level, I would add them, but Konomi doesn't focus on that side.
Might be a fun idea for a side league though. Have everyone come up with a few concepts and I could build characters out of those. Not sure if there's enough interest for that though.
Either way I'll be watching intently, this is all brilliant, just wondering about the possibility of participating myself.
You are welcome to join as long as there are still open spots (which there are right now). It's honestly not that complicated once you get the hang of it, you just need to be dedicated to it and not drop the ball halfway through the season.