When you’re happy with your document built with canvas and you want to copy its content to Word or Google Docs, using the Copy button on top right actually paste the Markdown content. Which is not interpreted by Google Docs, even if you activated Markdown in the settings of Google Docs.
A workaround is to select all the content of the document (Ctrl+A or Cmd+A), copy and then paste.
I suggest that when clicking the Copy button, a dropdown appears to choose between copying the Markdown content or the (HTML) formatted content.