Nope, it's totally random, that's the fun. GTS (which is a separate option) on the other hand, you can search out what you are looking for and trade what they are wanting if you have it, or post one of your own pokemon asking for something else and if someone somewhere else in the world has it, they give it to you. Wondertrade is just totally random and the closest you see what you're getting is when the trade is actually occuring