If you must look at it backwards, assume as a given, the fact that we do choose.
Given also, the fact that God is first cause, which logically implies that there is no fact outside of his causation.
Then our choosing, and our choices are caused, whether directly or indirectly, by God's causation.
Given further, that first cause is with intent, i.e. God, and omniscient God at that, then all that he caused he intended to happen. It is not by mistake that Adam and Eve, and the rest of mankind (except Jesus Christ) have fallen into sin.
But if you still must insist that our choices are robotic if God determines (or 'establishes' them, as the WCF puts it), then go with your construction, but please find a reasonable logic that shows that God's causation provides, perhaps, an 'envelope' of fact within which our little notions of possibility and unknowable chance prevail over outcomes. That is, to me, anyway, a huge logical error to arrange that, even if put into an envelope, but it is monstrous to consider something coming to pass outside of God's causation. That is simple denial of his Omnipotence.