Hi,
The Canon PRO-100 is an AirPrint-supported model.
About AirPrint - Apple Support
This means that this model can be used without additional printer drivers, provided that the printer and the iMac are connected to the same network (Wi-Fi router).
Make sure that the printer is connected to the Wi-Fi network.
Connect an AirPrint printer to a Wi-Fi network - Apple Support
If the router supports it, the easiest way may be to use a push-button WPS (Wi-Fi Protected Setup) method for the printer connection to the network.
https://support.usa.canon.com/kb/index?page=content&id=ART168656
Once connected to the router, you will have to add the printer to your iMac.
Add a printer to your printer list so you can use it on Mac – Apple Support (UK)
See also the information in the AirPrint guide from Canon UK:
https://www.canon.co.uk/support/consumer_products/apple_airprint_guide/
If there is a problem with AirPrint device discovery, try a full power-cycle sequence in this order (including the router): Power off the Wi-Fi router, the printer, the iMac, and all other devices/computers. Wait two to three minutes. Power on the router. Wait two to three minutes. Power on the printer. Wait a minute or two. Power on the iMac. Finally, power on all other devices/computers.
If the printer is not using AirPrint, such as with a direct USB connection, drivers from the printer manufacturer will be needed.
https://www.usa.canon.com/support/p/pixma-pro-100
https://www.canon.co.uk/support/consumer_products/products/printers/inkjet/pixma_pro_series/pixma_pro-100.html
Reset the printing system on your Mac to solve a problem – Apple Support (UK)