If you know the URL to the form library and the form name, then you're all set.
Define a node in your canvas called FormUrl. Its value will be something like:
concat("http://<servername>/sites/<sitename>/<FormLibraryName>/",FormName,".xml")
I'm assuming the FormName is some field in the form, which is used by your data connection to submit to the Form Library. This FormName should not change with each submit, i.e. it would be determined on first submit only.
Then just include a hyperlink control using this URL. If you run into issues opening that link in the browser, come back and let us know. The exact URL might need to be tweaked.
Keeping it even simpler, just put the URL to the form library itself in the email (/sites///">http://<servername>/sites/<sitename>/<FormLibraryName>/).
Good luck!