Related to this question, apparently someone who is on a USA no-fly list will not be allowed on international flights between other countries, if they have a chance of overflying or diverting to the US. And it's understandable that airlines would check this as part of the immigration prescreening, since they have to do that anyway.
So several people suggested he fly from Europe to Canadian airports nowhere near the US, such as Gander, Halifax or St. John's. That's great, but if you flew internationally into St. John's, the only sane way to travel onward is flight.
They don't do immigration prescreening on domestic flights. So would he still get flagged/blocked if he attempted a St. John's-Toronto or Halifax-Vancouver domestic flight?