An American citizen would be entitled to a trial for the same offence, let's say. An American citizen would be entitled to a trial either in a court martial, for genuine offences against the Law of Armed Conflict, or in a federal civilian court in which that citizen would receive all of the rights and protections of the U.S. Constitution--full confrontation, compulsory process, all the things that a criminal defendant in the United States gets.
First of all, a juvenile would never be tried by a court martial because of the historical limitations on military jurisdiction to adults, which is part of our argument for why this military commission should not be applied to Omar. Tried in a federal court, a juvenile would receive the protections that all 50 states in the United States afford juveniles--that Canada affords juveniles--which is basically a special procedure to determine whether or not he should be tried as an adult. If not, he should be tried as a juvenile, and he should be tried as an adult only if that procedure makes that right determination.
So there are any number of protections that Omar would receive if he were an American that he doesn't receive in Guantánamo Bay. He would also, very importantly, receive the right to habeas corpus. If he were an American, he would be able to be in front of a federal court today--or, more accurately, years ago--to present some of these fundamental challenges to his detention and trial as a child soldier to a regular civilian court without having to go through the process of being tried by a military commission.
Not only are these trials and their procedures limited to non-U.S. citizens, but the U.S. government takes the position that since they occur at Guantánamo Bay, the U.S. Constitution literally in no way, shape, or form applies to protect these people. In Omar's case--and in the case of other detainees at Guantánamo Bay--what that means is that they can be tried for offences that did not become part of the law until literally years after the conduct took place. Omar is being tried for offences under a statute passed in 2006 for conduct that he allegedly engaged in in 2002. Again, the U.S. government says it can do that to him because he's a Canadian citizen and not a U.S. citizen.