Would Gen. Flynn have a case in civil court?
Yes. Withholding exculpatory information can be considered a violation of civil rights. It is also abuse of authority under the color of the law as law enforcement are mandated to notify the court and the defendant of exculpatory information.
The Flynn case has been the most troubling to me. His disagreements with the previous administration made very powerful enemies in DC and I still think his “plea” had more to do with his son and not anything that he did, but that is only a guess based on what little we know.
Hopefully the truth will prevail and if there has been an injustice it will be made right.
Brady violation
It seems to me that it’s a case of entrapment and coercion.
I think you are correct here. I also think the sentencing is not a foregone conclusion yet. The judge must accept the plea bargain before the sentencing. If the bargain falls through the judge may direct that a trial be held. In such a case, the prosecutor may drop the charges "in the interests of justice". It would look bad for the prosecution but not as bad as if a sentencing occurred, exculpatory evidence appeared and it was shown that the prosecution knew about it all the time.