Do not be too nervous. Basically your explaining your relationship to strangers. Do not be upset with any questioning, as they have all information. So they see both sides. But your job is to prove that the visa officer made an error by refusing. Hopefully your wife and you prepare. My husband and I already knew all the answers my lawyer prep us for. Then he pick a few to focus on for my testimony. The Ministers counsel ( I said Judge before) and Canada Border Services Agent guy both can ask ask any questions and cross examine your answers. It is all for clarity. Same with your spouse. And when they ask at end what will you do if you lose the appeal. You can't say that you will keep loving each other and visiting or you will live togther in another country. You must be clear that you will reapply, a loss will not be tolerated.