WordPress image thumbnail removed whitespace

That would depend more on the image editor installed on your server than on WP. I’m skeptical that it’s possible in most cases. The client side solution offered at SO would be horribly slow and inefficient. Using the server image processor that WP uses to crop and resize is the way to go if it’s at all possible. With the GD editor (most cases), I doubt it. If your server has ImageMagick, there might be a way.

I’m surprised you have so many images with unused canvas, it’s not something I’ve run across very often. I guess it depends on your image sources.