You may have fixed this by now, but the two plugins are named:

EZPRPIO1.8LI
EZPRPIO2.8BF

and are in the folder

EPP_PRO

The latest version appears to be V1.5, and can be found at:

http://software.canon-europe.com/software/0030673.asp?model=

The installer still does not see CS4, so you may need to have an earlier version of Photoshop installed to install EPPP to, so you can copy the EPP_PRO folder across to CS4

As a long time user of PS, I still much prefer to use EPPP as it bypasses all the colour managment problems - my only gripe being controlling print size, (most of my prints are for competition use and need to fit a matt cutout) but there is a work around.

> Set image size in PS with resample turned off.
> then set canvas size to the paper size you are printing on,
(with a white background).
> Open image in EPPP and click on the SET button under COLOR ADJUSTMENT
and set the extension value to None
> Use borderless printing in EPPP

It still is not quite as accurate as printing directly from PS, but it's very close.

[EDIT]
Well there's a thing... I found and installed v1.5 as I went through the process of putting this message together, and have just looked to see what is new from v1.4 that I was using before. Previously it was impossible to set the border size in bordered (full) option to anything less than the default. You could only larger mmaking the print smaller. That has been fixed with v1.5, so my workaround above hs been made redundant.

--
Trevor
http://www.flickr.com/photos/trevor-dennis/