You COULD use epoxy provided you used an epoxy meant for repairing wood so that it would cure soft enough to sand relatively easily.
If it were me, I'd probably recommend you use a product called "water putty" that you should be able to find in most hardware stores. Water putty comes as a powder that you mix with water to make a paste that can be spread onto wood to fill holes or gouges. In fact, it's commonly used as a wood filler in manufactured plywood. When they cut a knot out of one of the exterior plies, they fill it with water putty and sand smooth. So, if you want to see what water putty looks like, go look at some G1S (Good on One Side) fir plywood.
Water putty doesn't shrink as much as other wood fillers as it dries, dries to about the same hardness as a softwood, sands easily and is paintable when dry. And, you can keep what you don't use for many years. It stores very well if kept dry.