I am wondering is it possible to have scale bar and north arrow in 3D view when viewing in browser and also when saving image.
Not super practical but It is possible.
Use View -> Decorations enable north arrow and scale bar. When you create 3d model it will "burn" Decorations on the surface.
If they do not have to be too pretty, you could create them as a layer(s) that could be exported to Q3JS. Bear in mind that a scale bar would be a bit misleading due to perspective distortion of distances