Making Desktop App Run on Web.

My experience with GL is limited to running fixed function pipeline on Windows workstations and imac. I have an OpenGL/C++ application running on Windows made up of about 10,000 lines of code. My customer has been asking about creating a version that could be run over the web and on tablets. Could both of those situations be handled by converting it to WebGL? How difficult would this be? My geometry is handled with display lists. There are as many as 2,000,000 polys on the screen at a time. Could that be done on a tablet? I can write a simpler version of the app that waters it down from 3D to 2D, using a few images in place of the 3D models. Anyone ever take an app of this size or larger and ‘port’ it from Windows to WebGL, Android, or Mac tablets?