If Hyman falls back down to Earth next year, just as Nugent-Hopkins did last year following his outlier year with McDavid, are his goals from the previous year going to help Canada win? It isn't that hard to make a case for Lafreniere over him given role and room for growth. Realistically Canada could take both, or neither, and it wouldn't shock.
Regarding Marner, Canada has a long history of cutting elite playmakers who don't factor into one of the top scoring centre spots. He may make it but if he doesn't no one should be overly surprised. Some players that Canada regularly cut in their primes: Denis Savard, Steve Yzerman, Ron Francis, Adam Oates, Pierre Turgeon, Mark Recchi, Martin St. Louis, Claude Giroux.