I have thought about Architect quite a lot and I'm pretty convinced that his ancient magister. Everything fits too well for it to be coincidence, I mean he's basically like Corypheus with the look, magical power and aura, just personality and memories are different.
It'd be very intresting to see what the Architect will do when he finds out what he was or when he regains his memories. He seems to genuinely care about darkspawn and their future, he's pretty much only pro-darkspawn character we have in the series
In other hand it's possible that he has been just tricking us to believe that and he has known what he is all along. I think this is less likely, but still possible.
Also I think the Architect and Corypheus have different kind of skills. Corypheus has very similar skills as old gods, ability to influence darkspawn and wardens with calling and body-hopping, but the Architect at least seems to lack the calling since he during book and games seemed to have some authority over darkspawn like by his presence forbid them to kill someone, but that seemed to be mostly cause darkspawn avoided and kind of feared him, not because he can influence their minds. He doesn't seem to have any control over Wardens minds.