We use dish soap in water to drown stinkbugs, a house pest, not a pool pest. It does work very well to break surface tension. IMO, 2 teaspoons dispersed over the entire surface area of a backyard pool aren't harmful to the pool and if you do wind up with some minor soap bubbles, that sounds far preferable to the water boatmen infestation. I'm surprised you have them in Canada. I always thought they were more of a warm climate creature. We haven't seen any here in our pool, knock on wood.

One thing: with such a large amount of water insects they obviously have a food source in your pool water. What is your water chemistry like?