Before you go any further, did you test if your application works on top of Mir itself - before snapping it up??
To do this, on your Ubuntu desktop, install “miral-examples” and “qtubuntu-desktop”, and for testing purposes “qtbase5-examples”.
In one terminal, run
miral-kiosk - you should see a black window pop up.
In a second terminal, run
you should see an analogue clock appear inside the miral-kiosk. That verifies that Qt and Mir can work together.
Now, to test your internal Qt application, run it from command line, making sure to specify
first. You application window should appear inside the miral-kiosk and be functional. If not, then you need to learn why not.