I believe David Gaider has said they will never deny or confirm the existence of the Maker.
Which means in the end, its gonna come down to what you (or your game avatar) believes.
For example, I am a Christian and i can see loads of similarities between the Maker and God himself. So i believe (as my avatars do) that the maker do exist.
For someone who doesnt believe in God in real life, they can just as well believe that the Maker in the game doesnt exist. And neither the believers nor the non-believers will be "wrong" about it.
To me Andraste is a clear Messiah, probably the last person to whom the Maker revealed himself physically/metaphisically, and any believer post Andraste will have to rely on faith when it comes to the Maker. Kind of like Jesus coming to Earth to save mankind, and from then on, God did not reveal himself to mankind, because Jesus became the bridge between God and mankind (Andraste is the bridge between the Maker and Thedas). And only a very few, very faithfull people will see a spark of divinity post-Andraste. Leliana being one of those few, she presents herself to the Hero of Ferelden as someone who had a dream sent from the Maker that compelled her to find the HOF and help him on his journey. By the time she meets the Hero, he's kinda still a nobody, who just came out of the battle in Ostagar, and yet she already knew he would be someone special with an important mission.
As for the Old Gods and Elven Gods, I kinda see them like Angels. The Old Gods were cast out and turned into Archdemons (like the angels turning into demons when they left Heaven with Lucifer). The Elven Gods tho its what been puzzling me the most, I still cant understand if they are powerful and god-ly because they were always so, or if they were just normal ancient elves who achieved such power and status. Either way, I think all of them have some connection to the Maker (in my second playthrough that i just started, im gonna be paying attention to all interactions with Solas to see if he slips on what he believes about the Maker, there could be a big revelation hidden in some small banther that at first we wouldnt give a thought about)
So what i believe in the game, its that the Maker is real, that Andraste was his last atempt at mankind's redemption, and that Thedas now has to take care of itself. The Maker might still work through certain individuals tho, but never directly. Either Andraste, Justinia, or just a good spirit, i believe the golden spirit woman in the fade was sent to help the Inquisitor. She was certainly not sent by the elven gods - they are too busy harvesting souls apparently - she was not sent by the old gods - still archdemons or trapped - so that leaves only 1 entity with enough power to do so - the maker himself. I dont believe she was Justinia tho, if she was, why wouldnt she say so. We already know spirits can stay in the fade lingering after they die (you can see the mother of that mage girl staying in the fade waiting for her daughter to come of age so that she can approach her in the fade - this is in one of the comics), so if that was indeed Justinia waiting to guide the Inquisitor throught the fade, why wouldnt she just say so?
There are many things in the lore that seem to indicate that the Maker is indeed real, but there is never any tangible way of proving it, and i think thats because the writers want to give the players freedom to believe or not. And never get to the point where you dont believe it throughout all the games and reach the end and - oh dang! - i was so stupid for not believing. Or the other way around.
Whatever you, as a player, believe about the Maker, it is a valid belief.