If you are using WiFi, you can use "AirPrint" from any Apple device. That sounds like what you are doing when printing from your iPad. I use AirPrint to print to my wife's Brother laser printer. My wife also uses AirPint for printing to the Brother connected (USB) directly to her MBP.
I connect to my Canon ink jet via USB. It is then shared on the local WiFi Network.
Apparently, the last time I did a Security Update, I failed to check that the USB Canon was still listed/checked in the Printers & Scanners System Prefs.
Thanks to you, it now is, which will make her happy.
Back to your problem...
Sometimes the list of Printers gets "confused" and thinks one of our two is busy/printing/etc. when it is not. The easiest fix for these non-Apple hardware devices is to just open System Prefs, select the "missing" Printer and delete it (using the minus button). Then turn around (once is usually enough, left or right is OK) and click the plus button and wait for the OS to "see" that Printer again.
I'm not sure of the settings/connections on your Canon, but I don't see any problem with Sharing it. You have several choices about sharing via the "Sharing" Pref. Enable "Printer Sharing". Look for it to show n the "Printers:" list. Decide who gets to use it in the "Users:" list just to the right. For Printers, you probably have only two choices: Everyone "Can Print" or "No Access".
I suspect that if your friend and you are both using CrownePointmain, he will be able to see your Canon, otherwise, he couldn't actually print to it. You can try using the "No Access" and see if that prevents him from printing, hopefully, he cannot (nor anyone else on the CrownePointman" network) even "see" the printer.
Just for info, how about a screen shot of your
both your "Printers & Scanners" and your "Sharing" System Prefs windows. Might be good to see those same prefs from your friend. You may need more than one post to upload all four images but you can also reduce their sizes using Preview if you don't have any other graphics editing apps.