C++ components of 3D Slicer Qt Loadable Modules (Module Overview — 3D Slicer documentation) are wrapped in python and exposed automatically (mostly). These wrapped python components will be available in Slicer and can be used by other modules.
I would recommend that you try to integrate this C++ code as part of a Loadable Module. It is also possible to have a sort of hybrid module, where Scripted module (Module Overview — 3D Slicer documentation) can include some C++ components (an example of this approach is one of the modules of Slicer-Liver: Slicer-Liver/LiverSegments at develop · ALive-research/Slicer-Liver · GitHub)