How to open *.cr2 files at Linux? Simple: install ufraw:
sudo apt-get install ufraw gimp-ufraw
Now, open ufraw (press ALT+F2 and type ufraw) and load the cr2 image. Then in the right bottom click at the Gimp button. Gimp will be launched and loads you image.
If you're interred on HDR effects, try qtpfsgui.