I am not aware of a coating that will be effective in leveling out the dips in your plywood deck. Since you are planning on coating the deck, I recommend that you pull up the plywood and repair the foundation of the deck to eliminate the dips and then install new plywood to the deck. You can then choose a number of textured coatings that will waterproof the deck. A urethane based deck coating with a non-skid texture would likely be something that you could apply yourself if that is what you are looking for. You may want to get a contractor to examine the deck and give you an estimate for the work that you want to have done.