I think that any such prosecution would face almost insurmountable hurdles.
First off, the charge requires that the accused has to have “assists an enemy at war with Canada, or any armed forces against whom Canadian Forces are engaged in hostilities,”. The difficulty here is that the forces in Afghanistan were irregulars.
What does an “enemy at war with Canada” mean? Does it mean all Afghans? Clearly not, because the Afghan government supported the military activities of the NATO forces in Afghanistan. Who exactly was Canada fighting against? Is “al-Qaeda” an enemy in that sense? If so, can the Crown prove that Khadr was acting for al-Quaeda, or was he acting for some other group? Was it simply a loosely organized resistance group, that didn’t take any orders or commands from any other group, like al-Quaeda? And, the Crown would have to prove that that group of irregulars was part of such a larger group in an operational sense. And, the Crown must prove these points beyond a reasonable doubt. Where does the Crown get that evidence, if everyone in that group was killed except for Khadr himself, 13 years ago?
Same for the second part of the offence: “any armed forces against whom Canadian Forces are engaged in hostilities”. The fact that the Americans were fighting against that group doesn’t mean that they were necessarily engaged in hostilities with Canadian forces. Were there any Canadian Forces in the area, engaged in hostilities with this particular group? Was it part of a larger organization that Canadian Forces were fighting, or was it a small cell of resistance fighters that were essentially operating on their own? Again, the Crown would have to prove this element, beyond a reasonable doubt. What witnesses would the Crown have in support of this part of the charge?
Then there’s the procedural requirements of the Youth Criminal Justice Act, which require that any young person who is under investigation can only be questioned in the presence of his counsel, a family member, or some other adult that can look out for his interests. The US did not do that, so anything he may have said at Gitmo is presumptively not admissible as evidence.
Then there’s the witnesses and the accompanying disclosure obligation on the Crown.
First off, the witnesses against Khadr are going to be almost exclusively US military personnel. How does the Crown get those people to testify? A Canadian court cannot force an American in the United States to come to Canada to testify. There are mutual legal assistance agreements between Canada and the US, but those agreements are discretionary. Canada cannot force a US citizen to come north if the US government does not support it. Why would the US government agree to send its military personnel north for the trial? But if the US does not, the Crown has almost nothing to base a charge upon.
Then, even if the US agrees to send those witnesses north, the Crown is required to disclose all of the witnesses that will testify in the Crown’s case, and to give disclosure of all documents, can-says, and so on. Those documents are almost entirely in the hands of the US government. There is no way for Canada to compel the disclosure of those documents from the US, and it strikes me as highly doubtful that the US would disclose the documents. But if the Crown does not provide that disclosure to the defence, the defence would be given a very strong argument that the trial is unfair. (Note that the Crown might argue that the disclosure obligation is met by providing all the documents in the Crown’s possession, but I still think that defence counsel would have a field day with the lack of disclosure.)
And even if the US agrees to disclose at least some of the documents, there is at least one document that would pose a major difficulty for the Crown. The report drafted by a senior office a day after the firefight said that the person who threw the grenade which killed the US soldier had also died in the firefight. If so, that exonerates Khadr. However, the US military changed the wording of the document several months later, to leave it open that it was Khadr who threw the grenade. That change in such a key document would give a defence lawyer a field day. It would also have a knock-on effect on other US documents: each time a new document is introduced, the defence lawyer would say, “we already know that the US military altered one key document; did you alter this one? And if you say you didn’t, why should we believe you?”
And finally, there’s the fact that the Supreme Court of Canada has already ruled that the US detention of Khadr did not meet Canadian standards for the detention of a young person charged with an offence, and that Canadian officials with CSIS were complicit in the US interrogation policies in the case of Khadr. The SCC has held that the federal government infringed Khadr’s rights under s 7 of the Charter by assisting the US interrogations at Gitmo. Given that finding by the Supreme Court of Canada, I would think there is a very strong argument that the defence could successfully apply for a stay of proceedings under the Charter.
When a Crown prosecutor is considering whether to proceed to trial on criminal charges, one of the factors that must be considered is the likelihood of a conviction. If a conviction is highly unlikely in a particular case, then the Crown has a professional obligation not to proceed.
Given all of the above difficulties, I think a Crown prosecutor would be hard-pressed to conclude there was a reasonable likelihood of conviction, so would likely recommend that no charges be laid.