It seems like my attempt to uninstall Tk::Canvas had uninstalled all of Tk.

Yes - I see now that Tk::Canvas is part of Tk. (I had assumed it was a separate distribution, but it's not.)

You firstly need to find out how to deal with this DOS attack that Norton AV has launched. (I don't know how best to do that, but I would expect there is some way of telling the AV program to permit these "infected" files to be installed and executed.)
Then, re-running:

cpanm https://github.com/StrawberryPerl/Perl-Dist-Strawberry/releases/
+download/patched_cpan_modules/Tk-804.036_001.tar.gz
[download]

should be all that's needed.

Cheers,
Rob