Had all kinds of problems trying to figure out how to get my 2-sided print function back. Searched all over and found bits and pieces here on MacRumors for other printers but not for my specific printer. Felt I needed to pass the word on how to fix this problem on my printer to others. I'm running OS 10.13.4 High Sierra on a iMac and also a Mac Mini. this work-around worked on both. When I installed the latest Airport Extreme router which my Canon MG3122 (MG3100 Series) printer was attached to it forced a driver upgrade for this printer (to CUPS Print Drive Version 16.20.00). This broke my 2 sided printer function (2 sided print choice grayed out). Must have Duplex function turn on and that too was grayed out. This is how I fixed it for this latest driver: 1. Select: Print under File on top of Mac desktop (Any Web page in safari will do). 2. Select: Show Details 3. Open pulldown menu that says "Safari" 4. Select: Print Features 5. Scroll down and turn ON duplex Printing function. 6. Scroll down further to "Duplex" function and from drop down menu select "Duplex - Long Edge" 7. At top of printer details page select "Presets" function and "Save Current Settings as preset" 8. Name the new preset as "Portrait (Duplex) 2-sided" (or some other name that makes sense to you). Anytime you need to print 2 -sided select this new preset configuration. Done!