Asymmetrical cheek muscles, what can I do to make my cheeks match?

Your case is somewhat unique and would need an in-person assessment to properly diagnose and recommend a treatment plan. While the area you are referring to is indeed dynamic, there are formulations of dermal fillers today that are specifically designed to move with your face. However, a careful evaluation would be needed to determine whether this is the right approach for you. I advise you to schedule a consultation with an experienced, board-certified dermatologist who will have the expertise to customize a treatment for you to produce the best possible results. 

I believe the intradermal microinjections using Restylane Refyne will help with this issue as would Sculptra Aesthetic. I know it is not what you want to hear but I think it will help.

This is really an interesting case. As it is dynamic it is really difficult to tell from a photo just want is occurring. It could be just a volume loss or more likely the area is bound down. Which unfortunately means you really need someone to closely evaluate the area . I know you mentioned not wanting to use a filler but an experienced injector can really make a difference in this area with a filler. Today there are dermal fillers that are more elastic  and function very well in dynamic areas.