User blog comment:DeadpoolN7/Mass Effect 4/@comment-3430127-20121016130500/@comment-1504310-20121016135910

I doubt it will take place after because of this comment, or at least not a story that takes place after yet: 'Casey Hudson commented that Mass Effect 3 "will be easier [to develop] because we don't have to worry about continuity into the next one'

I'm sure after some time passes they will decide on a Cannon ending like they have with the past two games as well as some older minor things like Revan being Male or the Exile being Female ya know, but for now I'll take that statement to mean it will be a pre-quel or take place in between/during Shepard's trilogy.