How can you program a dotNet Windows (or WPF) Application in order to let it going fullscreen on the secondary monitor?
For WPF apps look at this post. Ultimately it depends on when the WindowState is set to Maximized. If you set it in XAML or in window constructor (i.e. before the window is loaded) it will always be maximized onto primary display. If, on the other hand, you set WindowState to Maximized when the window is loaded - it will maximise on the screen on which it was maximized before.