You will never be able to open your raw files from your new camera in CS4.
You need version 8.7.1 of the Camera Raw plug-in (ACR), which only runs in CS6 and higher.
You need to locate, download, install and run the free, stand-alone application Adobe DNG Converter on each batch of raw files from that camera, in order to convert them to raw DNG files that can be subsequently opened by ACR in CS4.
Remember you need to launch and run the DNG Converter on each folder (not files) containing your Canon raw files. THe DNG Converter doesn't do it magically for you just sitting on your HD.
Or you can upgrade.