This is a general informational post meant for those dealing with similar problems.
I really ran into 2 problems with this setup, so let’s start with the networking first. The scanner worked fine over the wireless network, but I had to reset the router since it was set to work as an AP, and we needed the router capabilities to add a guest network.
Setting this router (ASUS RT-N66U) to router mode enabled 2 separate subnets, one for WAN and one for LAN, which gave the printer the IP address 192.168.2.x instead 192.168.1.x and prevented the scanner setup utility from finding the scanner on the network. I wired the scanner into a hub and then set up a hub to plug the router into so the computer next to it would get a 192.168.1.x IP address while the router can continue on 192.168.2.x.
Then I ran the scanner setup utility and it added the scanner no problem, but when I opened the MP Navigator scanner application included by Canon, scanning always failed and returned error code 5,145,61. I reinstalled, changed the active scanner in the network scanner utility, all to no avail. I went back to the printer and printed out it’s LAN Configuration information and sat back at the computer.
Finally, I opened the MP Navigator application again and entered the scan photos dialogue, then clicked on the preferences button at the top right of the window. In the product name dropdown you’ll see MX870 series (Network:xxxxxxxxxxxx) where the Xx represents the MAC address of the connection type (LAN will have one MAC address, and wireless will have another). In this case, it turns out that even though I had selected the correct address in the scanner setup utility, the application preferences were still trying to use the wireless MAC address of the scanner. Since it was connected to the wired network, this obviously caused it to fail.
The solution is to click into the dropdown and find the mac address that matches the LAN settings printed out (it should be the only other available option.