Selecting GUI backends

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How can one select the GUI backend using OpenCV and Python?
If I install opencv with conda (conda install -c conda-forge opencv), I get the QT backend:

GUI: 
    QT:                          YES (ver 5.12.1)
      QT OpenGL support:         NO
    Win32 UI:                    YES

But, if I install opencv with pip inside (pip install opencv-python), I get the something else:

  GUI:
    Win32 UI:                    YES
    VTK support:                 NO

How can I control or select which backend I want?