Hunter would be 20 and it's a U20 tournament so he isn't eligible. Part of the reason he played through a tough injury last year was because it was his last chance to make the junior team.
McCann wasn't invited to the summer camp but can still get an invite to the one in December if he plays well enough. By not getting the invite for the summer camp, he doesn't get the extra time to get familiar with the other players, coaches, systems, and show the staff what he can do.