Natural law is greater than even Canon law. 
We cannot make a canon law that conflicts with natural law.

Marriage was created by God "from the beginning".

As Jesus tells us in St Matthew's Gospel. 

Pope Francis isn't "going back to the Gospels' at all...in fact some commentators are totally perplexed that he refuses to wrestle with Jesus's own words (and his correction to Mosaic law) in St Matthew's Gospel.

He ignores it!!