I am an IT professional and also had some challenges with the IP8720's new wireless setup. Some of this advice may help with other models.
My understanding is that this model communicates only over the 2.4Ghz wifi bandwidth. As a result, some newer Wifi routers may either be dual band (both 2.4Ghz and 5Ghz) In my case, I have a Google Nest Wifi setup. This defaults wifi devices that have 5Ghz to that band. The laptop I used to setup my fancy new Canon printer was on 5Ghz. A known workaround to force a device to 2.4Ghz is to make it join the Google Nest Wifi GUEST network.
Here's where the fun and trickery begin. In order to get the laptop AND the printer to perform the initial setup using the final PRIMARY wifi SSID (Wifi network's name) and password, you have to trick both devices into joining the GUEST network to force 2.4Ghz and the laptop and printer to play nice with each other. Here's the important part...you have to TEMPORARILY give your GUEST wifi the exact same SSID(Network name) and password as your PRIMARY network. To do this, it's a few steps.
1) From your mobile phone, Open Google Home App. Go to Wifi. Click gear icon in top right.
2) Write down both your PRIMARY network name and password for later
3) Tap GUEST Network, Manage; write down your GUEST network and password as they are. Click the back arrow at top left to return to the Primary network screen. Click the gear icon at top right
4) Temporarily rename your PRIMARY network: whatever it's called, delete only the last letter. Same for the password because Google Nest Wifi makes sure that your PRIMARY and GUEST networks don't have the same password. Good practice. Click SAVE. If you need to, write down the new SSID(Network name) and password (with the last characters temporarily removed)
5) Click on Guest Network, Manage
6) Rename your GUEST network name to the original PRIMARY network name and original full password (original full name/PW from step 2) , click save
7) From your laptop you're using to setup Canon PIXMA IP8720, ensure your wifi is connected to the normal network name you use that is now being temporarily forced to your GUEST network to be on 2.4Ghz
8) From here, restart or continue the Canon setup. Your printer should now be detected.
9) After setup completes fully, from your mobile phone, open Google Home app, wifi, scroll tro bottom, tap Guest Network, edit the guest network name back to it's original values from step 3, save
10) wait, click back arrow to reutrn to Wifi screen, tap gear in top right. Revert your PRIMARY network to the original values from step 2, save, wait
11) You may have to power printer off and on to get wifi light to return to steady blue.
NOTE: During this process all/many of your devices in the house will lose wifi/internet connection. Let everyone know it will happen before you start to prevent outage rage 
I hope this helps some of you out there. Similar approaches may be followed using mobile device wifi hotspots to spoof your wifi's primary network SSID and password. You will have to power off your router and access points during that time so the hotspot is the only SSID on with that name and password. Have your laptop join that hotspot wifi network and run setup to reach the printer.
This is just some of the tech fun that comes with changing technologies. In this case, a printer with 2.4Ghz only and newer wifi with dual band (@.4 and 5ghz) that don't play nice together. I hope your printer makes some great pictures!