It will be different, depending on the weapon. 2-handing a weapon does two things, it increases your strength by 50% and it increases the hidden damage multiplier for your attacks.
So, if you 2-hand the weapon without enough strength to wield it 1-handed, you will get the same scaling bonus as you would if you wielded it 1-handed with sufficient strength. But, you will do more damage 2-handed, because of the hidden damage multiplier.
For example, with the Black Knight Greataxe I had an attack rating of 623 1-handed and 643 2-handed, which was caused by a small boost in stat scaling. But, the 1-handed damage was 361, while the 2-handed damage was 500, a big boost caused by the hidden multiplier.