I have heard that the Bible says that Jesus suffered at the hands of the Romans like no other person in history. If this is true and He forgave the Romans who crucified Him without them asking for forgiveness then why must we assume that Hitler was not forgiven without asking for forgiveness? He said that the reason that He was asking for forgiveness was because they didn’t know what they were doing. If they didn’t did Hitler?
The term used in Greek there (which would be “from-let” in English) can, colloquially, mean “excuse” as well as “forgive”; “pardon”, in English, is a better translation in some ways, because it can similarly be used either way.
The context of GosLuke’s report there indicates the “excuse” sense of “from-let”, or “let off” as we might say in English. I don’t think we can say it was forgiveness in the sense related to repentance.
So who was Jesus talking to?
Obviously to the Father, not primarily to the ones crucifying Him.
Which again lends weight to the “excuse” instead of “forgive” side of the meaning. Forgiveness is a restoration of personal communion between the one who has sinned and the one sinned against. That communion obviously wasn’t being restored at that moment! (Though the centurion in charge of execution seems to come to some significant faith in Christ toward the end.)
I would say, in answer to your original question (which I never got around to opining on, sorry 
): I have no doubt Christ excused and excuses everything that can be excused, in regard to Hitler or to anyone else. That’s what a perfectly just (fair) and loving person would do. But as C. S. Lewis once put it (following MacDonald as I recall!), once all the excuses are cleared away, what’s left over still involves and requires forgiveness.
From what is archived regarding Hitler, which is a lot, I think I can say with some assurance that he knew he was cheating (to put it mildly). That isn’t someone with excuse in what he is doing; and while he doesn’t need to repent before God will love and act to save him, he’ll still need to accept repentance (if I may summarize several things shortly that way) before God’s forgiveness and salvation can be completed in him. (Even though from God’s perspective He sees Hitler’s salvation as finished already, as naturally God would, being God and so both above and ever-presently in contact with all natural history, including Hitler’s personal history. )
This seems to be saying that God can’t forgive without my permission? What am I missing?
If you are the one that sinned and I am the one sinned against, can’t I forgive you without any knowledge on your part? If not there’s a whole lotta folks messed up on this forgiveness thing. What if a person dies before I forgive him? Am I doomed to live a life of unforgiveness?