I have a quick question. IS it possible to sell my game commercially to Steam, and if it was created in unity3d free but not the pro version?
You don’t sell anything to steam.
You sell something through Steam (its a publishing platform).
And that can be done with Unity as well as Unity Pro 
But assuming you would be required to implement the base of steamworks into your game, you require Unity Pro as you can not use plugins in the free Unity at all