Canon printers have never really gotten along with Macs. I wish I knew that before I bought my i9900 at home and Pro9000 at work. Apparently for instance, ou can't print over the network. Things are a little better with the Pro9000, but apparently, it is very difficult to get them to work off the USB port of an Airport Extreme. "Apple Discussions" reports that this is a big problem. The apparent solution is from http://discussions.apple.com/thread.jspa?messageID=6648645
Download the very latest Canon drivers. these are dated December 2007. There two versions, one is a CUPS driver and the other regular. Apparently you use the non-CUPS one at Canon
When you add the Canon Pro9000, add it as a generic Canon IJ Printer rather than the specific Pro 9000. No one knows why this works, but you remove the Printer, then add it again. You fix this in the Print Using field
Discussions.apple.com mentions that there is a generic problem with printing from an Airport Extreme base station which recommends using "Apple's Printer troubleshooting":http://docs.info.apple.com/article.html?artnum=107418 that is pretty generic and involves just checking the Airport Extreme sees it and deleting the printer queue on your Mac. But some say the generic issue is that the Airport Extreme Base Station sends too much down the USB port (no flow control I guess) so it overloads it. There is an Applescript that tries to slow this down called "AirPrintFix":http://www.macupdate.com/info.php/id/24661 which you make a startup item as the "author":http://www.macosxhints.com/article.php?story=20070118020953464 described to Macosxhintg.com. He used a tool "Eavesdrop":http://www.baurhome.net/software/eavesdrop/index.html which listens in on a TCP connection over your Ethernet.