Hi,
regarding Mono at Linux, there is some work in progress and a prototype:
https://bitbucket.org/chromiumfx/chromi ... no-support
The core CEF wrapper (ChromiumFX.dll) works but without the remote layer. The webbrowser control implementation (ChromiumWebBrowser.dll) doesn't work.
It's far away from "supports Linux", and I won't be able to work on this anytime soon.
Regarding transparency, I never tried. But whatever you can accomplish with native CEF, you should be able to do with ChromiumFX as well.