Again, I'm not a Canadian-trained lawyer; I can't speak to the Canadian law.
I didn't testify that he couldn't be tried in Canada. I think it would be inappropriate to try him in a civilian court; he's a military detainee. I wish I could speak to it. I really am not familiar enough with Canadian law. I couldn't say whether he could or couldn't be prosecuted under Canadian law. I'm sure there would be great difficulties--certainly evidentiary difficulties--that are taken into consideration in a military tribunal that I presume wouldn't be taken into consideration in a Canadian civilian court. To me, that would be the biggest bar to any conviction.
As to what he could be charged with, I presume Canada has some statutes that relate to aiding and abetting terrorism. Perhaps he could be charged under those, but you would have to ask a Canadian lawyer.