Do you want to import raw files into iPhoto? .cr2 files can be generated by several different Canon cameras. What is the model of your camera? iPhoto cannot open all .cr2 raw formats.
For a list of supported cameras in Mac OS X lion and Mt. Lions see:
If your camera is not supported by your MacOS version, use the software that came with your camera to develope the raw images and to export them in a file format that iPhoto understands, e.g., tiff or high quality jpegs.