Rather than plywood, which can be warped, especially in 4' long pieces , I prefer to use melamine board. It's perfectly flat and the sealed surface protects from water damage.
Also, another point from my experience. In the case of this dresser, I would be concerned about the base on the floor being smaller than the aquarium on top. Most bow front tanks are generally tall, making this combination even more prone fall over. To be certain of my evaluation, I would want to see a pic of the stand with the aquarium sitting on it.
Aloha,
Mark