Ed has an iPad 4 and he can't print to his Pixma printer. Apple says he can't. Leo says that Apple uses "AirPrint" to print via WiFi, and if the printer doesn't support it, then he'd have to add additional hardware to give it that support. But there may be software that Apple offers for free. Otherwise, Leo recommends xPrintServer. It'll take any USB printer and make it an AirPrint compatible printer. But at $150, he can probably buy a new AirPrint compatible printer, unless he's needing a network capability for multiple printers.
The chatroom says that Canon has a firmware update for some of their printers that make them AirPrint capable. So he may want to check that out.
(Disclaimer: Lantronix xPrintServer is a sponsor).