In 2006, the US Congress passed the Military Commission Act which made it clear who has jusidiction over unlawful enemy combatants. Khadr is being tried by a military judge in a military court building on a military base, Guantanamo.

Like it or not, the Afghanistan War is a NATO operation with full participation of Great Britian, Canada and the United States. The UN Security Counsil did vote vote their support directly, but they sent a fair number of aid workers to assist.

The US has every right to try, convict and even execute a Canadian citizen (civilian) who kills an American soldier. It is not as if the Canadian government or the news media don't know about the trial. The man killed was a medic, by the way.