I believe that Demon Baby Morrigan is cannon whether or not it is your demon baby is a matter of preference.
I also understand that Bioware are working on something that will allow you to create the world you want before you start without having to directly import save games.
I've got a thread up with actual rumors of what's in DA:I, and one of the topics covered was the canon regarding the old god baby. If you haven't already seen the thread, you can click here to get there. It's got a lot of information. Anyway, if you don't use The Keep, then there is no old god baby.
The Keep is the method that allows you to create 'world states' (which is your history regarding DA:O and DA2). There is no way to import previous game saves into Inquisition. The Keep will be released either slightly before or at the same time as DA:I.