Go ahead and discontinue the Maracyn 2. In all honesty, it's not a super effective medication any more because many bacteria have formed resistances to it. When you get the Kanaplex, you can try to feed it but if you don't think he'll eat, even if it's soaked in garlic, it's probably best to go straight to putting it into the tank.
Is he being treated in the 5gal? If so, take out any carbon you may have in your filter before adding medication. For Kanaplex, treating in a 5gal is easy as it is 1 measure per 5gal. You can also continue using epsom salt while treating with Kanaplex.
Good luck with the little guy and keep us updated on how he's doing.