where can I find the WPS button on Time Capsule (for connecting to a Canon printer)?

There is no WPS button on the Time Capsule.

You might be able to get the printer to connect using the following method:

Open Macintosh HD > Applications > Utilities > AirPort Utility

Click the Time Capsule icon, then click Edit

Click the Base Station menu at the very top of the computer screen. Do not click the Base Station tab in the center of the screen.

Click Add Printer and then select the First Attempt method, then click Continue

The Time Capsule will search for you printer. If it finds it, click Done

If this method does not work for your pinter, you will need to follow the manufacturer's instructions for manually connecting the printer to the wireless network.

Sorry, there are no WPS buttons on any Apple devices that I have ever seen. The method that I described worked fine for my neighbor, but he has an HP all-in-one device.

I assume that you have powered off the complete network and then powered things back up in sequence starting with the modem first. If that does not help, I would suggest that you check with Canon support to ask them how best to proceed.