Gone With the Wind is indeed in the Canadian public domain. And it will be in the UK public domain on 1st January 2020. However, it will not be the USA public domain until 1st January 2032 since it was first published in 1936. And the lawyers for the estate are litigious.
However, I note that it's now at Gutenberg Australia. I don't know what arrangement they made with the estate, but I know
they received letters about it.