Penatrating oil spray, heat and puller .....
I have ran into this before take out cotter pin, take off nut and washer, soak the splines with foaming penetrating oil spray (Deep Creep or Power Blaster) a few times and then let sit over night. Next day heat it up not to hot that you take out your prop seal just enough to get the penetrating oil bubbling this may be enough to free it. If repeating this process still doesn't free it up now you need to use a puller if you don't have one go to Canadian Tire parts counter and they will give you one with a deposit equal to its value use it take it back and you get your deposit back. JMHO
Cheers Kevin