The actual fact is that God predestines people to be saved or remain reprobate depending on their free will choices. It is not that God predestines people's choices. That could happen if God was doing the predestining within the dimensional boundaries of our finite universe. But God exists outside of our 4 dimensional space time reality. This means that God can see the whole panorama of past, present and future choices, and is quite capable of planning a person's future based on his free will choices. This is achieved within God's infinite dimensional reality. He knows beforehand who will embrace Christ and who will reject Him, so, He is able to write the names of those who embrace Christ in the book of life.
This is what enabled God to harden the heart of Pharaoh through his own free will choices. In a sense, Pharaoh hardened his own heart through the choices he made, and God did nothing to alter that. He knew Pharaoh's future, that he will eventually end up drowned in the Red Sea along with his army. Pharaoh could have chosen differently and his future would have been different. There was nothing to stop him choosing one way or the other. But God already knew which way he would choose, so his future was predetermined.
This is an unknown to me. It could be the way God works. Scripture is unclear.
Things that would go against that idea are:
Gen 6:5-7 Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually. And the LORD was sorry that He had made man on the earth, and He was grieved in His heart. So the LORD said, "I will destroy man whom I have created from the face of the earth, both man and beast, creeping thing and birds of the air, for I am sorry that I have made them."
The above suggests that God did not "know" how bad man would become, and He wished He had not created man.
However, a similar idea to yours seems to be supported by the Early Church Father Iranaeus. Who suggests that within a framework of free will God still knows what will happen. See the following passage about Pharaoh.
Chap. XXIX. — Refutation of the Arguments of the Marcionites, Who Attempted to Show That God Was the Author of Sin, Because He Blinded Pharaoh and His Servants.
1. “But,” say they, “God hardened the heart of Pharaoh and of his servants.” (Exo_9:35) Those, then, who allege such difficulties, do not read in the Gospel that passage where the Lord replied to the disciples, when they asked Him, “Why speakest Thou unto them in parables?” — “Because it is given unto you to know the mystery of the kingdom of heaven; but to thorn I speak in parables, that seeing they may not see, and hearing they may not hear, understanding they may not understand; in order that the prophecy of Isaiah regarding them may be fulfil leading, Make the heart of this people gross and make their ears dull, and blind their eyes. But blessed are your eyes, which see the things that ye see; and your ears, which hear what ye do hear. (Mat_13:11-16; Isa_6:10) For one and the same God [that blesses others] inflicts blindness upon those who do not believe, but who set Him at naught; just as the sun, which is a creature of His, [acts with regard] to those who, by reason of any weakness of the eyes cannot behold his light; but to those who believe in Him and follow Him, He grants a fuller and greater illumination of mind. In accordance with this word, therefore, does the apostle say, in the Second the] to the Corinthians: “In whom the this world hath blinded the minds of them that believe not, lest the light of the glorious Gospel of Christ should shine [unto them].” (2Co_4:4) And again, in that to the Romans: “And as they did not think fit to have God in their knowledge, God gave them up to a reprobate mind, to do those things that are not convenient.” (Rom_1:28) Speaking of antichrist, too, he says clearly in the Second to the Thessalonians: “And for this cause God shall send them the working of error, that they should believe a lie; that they all might be judged who believed not the truth, but consented to iniquity.” (2Th_2:11)
2. If, therefore, in the present time also,
God, knowing the number of those who will not believe, since He foreknows all things, has given them over to unbelief, and turned away His face from men of this stamp, leaving them in the darkness which they have themselves chosen for themselves, what is there wonderful if He did also at that time give over to their unbelief, Pharaoh, who never would have believed, along with those who were with him? As the Word spake to Moses from the bush: “And I am sure that the king of Egypt will not let you go, unless by a mighty hand.” (Exo_3:19) And for the reason that the Lord spake in parables, and brought blindness upon Israel, that seeing they might not see, since He knew the [spirit of] unbelief in them, for the same reason did He harden Pharaoh’s heart; in order that, while seeing that it was the finger of God which led forth the people, he might not believe, but be precipitated into a sea of unbelief, resting in the notion that the exit of these [Israelites] was accomplished by magical power, and that it was not by the operation of God that the Red Sea afforded a passage to the people, but that this occurred by merely natural causes (sed naturaliter sic se habere).
