Your Netlify subdomain should not be visible to Google. It can index only what it can see. But you could set it up in Google Webmaster tools (verify via html-file) and then maybe disavow all pages in that Netlify subdomain?
But to be honest, that would be a perfect question to the Netlify support.
The canonical meta-tag is more for things inside of a domain like yourdomain.com/path1/title and yourdomain.com/path2/title is the same content (for instance single pages inside of tags)