I solved a problem that drove me crazy for a couple of days. Posting it here hoping it helps others.
I have an iMac running mac OS High Sierra and a Pixma MG5320, used both as a printer and a scanner. Both are connected to my home wireless network.
Everything worked fine until 4 days ago. Then, all of a sudden, I couldn't scan from it.
From Systems Preferences, I deleted the MG5320 and added it back. When I did that, I had trouble finding it on the network, and even when I could, it would only install as a printer.
I went to the Canon web site and downloaded the latest drivers. I installed them. I also reinstalled MP Navigator (I generally don't use it, but I thought it might help). I tried several combinations of reboots, uninstalling drivers and reinstallating them. Nothing worked. I could print, but I couldn't scan.
Last night I saw that Apple released the latest update to High Sierra (10.13.5).
When I went to the App Store to download it, I noticed that new Canon printer drivers had been installed in the background on May 30 I have it configured to autoupdate). There's a good change that's what caused the issues.
I updated High Sierra to the latest version, rebooted, deleted the MG5320 from System Preferences, added it back, and it worked on the first try.
Bottom line: if you are having issues scanning from your MG5320 after May 30, there's a good chance that upgrading to the latest point release of High Sierra will fix that.