To disable logging to the Canon.log file:
1.) Ensure you are using Ranger for CR-180 v1.5.0.3 or newer (available here http://opd.usa.canon.com/html/download/cr180.html), and;
2.) Disable Canon driver support for Canon.LOG by ensuring that the registry key:
HKEY_CURRENT_USER\Software\Canon Electronics Inc.\Canon Scanner Driver\Canon CR-180\General\Trace Log = 0.
Or if you'd prefer, just download the attached TraceOff.zip file, then extract and execute the embedded TraceOff.reg file.