I was able to fix the issue...for now...using the "Patch for Network Scan, USB Scan" provided by Canon under Support for my printer model. This was after uninstalling and reinstalling MF Toolbox using normal Windows mode, safe mode, and Revo Uninstaller; as well as updating the settings under Services > Windows Image Acquisition properties, Log On and Recovery tabs (none of which worked on its own).
Hopefully I won't be back on this forum again, as this is at least the third time MF Toolbox has suddenly lost the ability to communicate with my scanner despite the print function remaining consistent.