Have a look at Digital Darkroom section.
Beside this, you need the import filter for your camera. Although .CR2 is the RAW format of Canon they change it slightly for each camera. Check www.adobe.com and look for the RAW import filters. There are updates for earlier versions of Photoshop.
Alternatively you can use the DNG converter (also from Adobe) to convert the proprietary Canon RAW file into the royalty-free Open Source Format RAW file DNG (Digital Negative File). PS and other picture editors can open this format.