Unfortunately, not all printers are compatible with the printer server function of the AirPort base stations. Your Canon LBP 2900 may be one of them. I went to the manufacturer's support website and only found printer drivers for OS X 10.5 Leopard which is pretty dated especially if your running Yosemite. Note; however, that this driver is for the Mac.
To see if your printer is compatible, take a look at this iFelix Unofficial AirPort Printer Compatibility link. If your printer isn't listed, it doesn't necessarily mean it won't work, but simply that it has not been verified. iFelix also provides the following workaround for printers not on the list that would certainly be worth a try.
Also you can try this Apple Tech Support article to see if it will help: Printer troubleshooting for AirPort Base Stations and Time Capsule
Finally, check out this IBM support article to see if your printer is listed as having a Postscript or PCL3 interface. If it does, then it will most likely work with the AirPort's USB port. Printers that use the "HP LIDIL" interface must be connected to a computer directly and will not work.
