"do the courts in Canada not have the option of trying and sentencing juveniles convicted of serious crimes as adults"

Yes, they do - although the logic, as much as I can follow it, strikes me as inconsistent. But that aside, being tried in a Canadian criminal court as an adult would be vastly preferable to sitting for eight years without trial in Guantanamo, then being put through an extremely questionable judicial process, and then being sentenced to another eight years. I wonder if a juvenile - whether tried as a juvenile or adult - has ever been sentenced to sixteen years for murder in Canada? I doubt it ....