I might have completely got what you are saying, that doesn't mean it's the truth. This is not taught in Scripture at all. If the cross was not God's will, how could Jesus have saved people from their sins and taken away the sin of the world? The angel told Mary right from the beginning that Jesus would save people from their sins. How could his death have been prophesied by Isaiah and others? Jesus said that he would be lifted up just as the bronze serpent was lifted up in the wilderness - even Moses spoke of it. Peter says that we are redeemed by the precious blood of the lamb who was chosen from the foundation of the world. Why did Jesus predict his death and say that he, the Good Shepherd, was going to lay down his life for the sheep? He also said that he lay it down of his own free will and had the authority to do so. Why did he say that he came to give his life as a ransom for many, or pray "shall I say 'Father save me from this hour?' No, it was for this reason I came." (John 12v27) Why does Paul say that God was in Christ reconciling the world to himself? How could Christ have been our Passover lamb, and we be saved by his blood?
If God didn't know about the cross and it wasn't his will, what was it - some sort of mistake? That God actually wanted Jesus to achieve something different, but when people like Judas failed to co operate he thought "well I really don't want them to kill my Son but it seems to be happening, so I'd better resort to plan B and see if I can salvage anything from this mess"?
This sounds very much like Moonie teaching to me - they tell everyone that God's plan was not for Jesus to die but to get married, and that he failed because he got himself crucified instead. That God had to somehow think how he was going to use Jesus' death on the cross for good, because his will had been for something else completely.