Hello,
Not using the printer in question, nor the hub, but here are a few comments anyway.
You mentioned channel optimization. The automatic detection of devices and selection of channels can sometimes cause problems. Have you also separated channels, and given the networks different names? Would it be possible to use 2.4 GHz only, just for a test?
When all settings are OK, you may want to try the following power-cycling sequence: Power off the router, the printer, the computer, and all other devices (iPhones, et cetera). 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 computer. Finally, power on all other devices.
The Canon iX6850 is listed in About AirPrint - Apple Support as a model supporting the driverless AirPrint technology. This means that it should be possible to use your printer without additional drivers, provided the printer and the computer are connected to the same network (Wi-Fi router). The printer connection can be wired (Ethernet to one of the LAN ports of a router), or wireless.
