Plywood will be more sensitive to water than solid wood, but definitely better than OSB. Regardless of what you use you should have it sealed well but the edges are of particular concern.
My stand is solid wood, except the floor. I have a pond liner lining the sump portion up to about 1” up the walls, so that’s all covered. The rest is several coats of polyurethane. The front edge inside the doors I’ve had to touch up once.
For Plywood, I would use polyurethane at a minimum but an coat of epoxy on exposed edges that may be exposed to water might not be a bad idea.