If push comes to shove, the Americans could literally put him on a bus and send him north. He cannot be denied entry.
Why not just put him on an aircraft and push him out the door when in Canadian airspace?
The Canadian government can tell the world how useful he was to the intel community and how his contributions were essential in killing hundreds of jihadis and preventing scores of attack on Allied forces.
They can then go one to say how much they are looking forward to working with him as a free man in Trendy Toronto, much more convenient than Gitmo, and expect he will help them mop up sleeper cells in Canada.
Then drop him off in front of the most malignant mosque in Canada...