Hi again. Adobe finally got back to me. Here's what they had to say:
"Adobe supports AVI natively in Premiere Pro CS4, however, if the format is proprietary for Canon (ie they are using one of their own codecs) then performance on the timeline may be an issue.
Without knowing about the system your reader is working on, its also hard to say whether it's an issue with his system specifications. For playback of full HD content (1920 x 1080) we recommend a minimum of 4GB RAM, an independent hard drive to store and playback video footage esp if the datarate of the video is an uncompressed or low compression ratio. Not to mention the processor he is using.
We can recommend that if he wants it to playback better to use Adobe Media Encoder to convert it to a format that is more suitable for his system. (Ie P2 or H.264 for example.) There are also some updates for Prem and AME just released that improve playback etc which may give better performance on the timeline.
I would also get him to find out what codec Canon uses for the video files, what datarate the compression is at, pixel size and frame rate. I know that some cameras are using odd frame rates of 20fps which makes interpreting footage a challenge as it is not a standard frame rate to begin with."
...So, assuming your computer is up to the task, the problem might have to do with Canon's video codec. Let me know if you're still having problems and I'll contact Canon to find an answer.
