My recommendation is that any settings that will be the same for all courses be put in localOverrides.conf and authen_LTI.conf, and only things that will be different for an individual course be put in course.conf.
This leads me to the first thing to check: if $LTIBasicConsumerSecret is set in course.conf, then this is the value that will be used. Make sure that this string matches exactly what you set in Canvas. For debugging purposes. I would start with a secret that only involves numbers and letters. I don't think symbols should cause a problem, but this eliminates one possible complication.
A couple of other things:
Make sure that the consumer key is set in Canvas. It can be set to anything, but I know when I set up LTI, WeBWorK didn't like having a blank key.
Try the URL in Canvas with and without the slash at the end. I have mine set up with the slash at the end (i.e. https://webwork.yourschool.edu/webwork2/coursename/), but I can't remember how picky it is about this.