Double-sided Printing with iMac?

My Canon printer CAN print double-sided, but won't print from my iMac. My iPhone and iPad can print to it double sided no problem but the option for double printing is gray on my computer, Apple support is literally no help, what can i do?

It shouldn't be the issue, but I'd try either re-installing or updating your printer drivers for your model. Duplex printing should definitely be included, especially if you can already print to it from your iOS devices. Here's a link to a page with driver information on it