Another way of look at who has a chance to slot into the forwards line up is by looking at special teams. The bolded are projected to be or have been mainstays on the Leafs' special teams.
The 5v5 line up is going to include Martin who doesn't play either PK or PP. This, in turn, forces many of the Marlies on the cusp of making the lineup on the outside looking in. This is a general idea I've put forth as these lines can (and will) change day-to-day.
Hyman - Matthews - Nylander
Marleau - Kadri - Brown
JVR - Bozak - Marner
Komarov/Martin - Moore - Kapanen
PP (need 8): Matthews, Nylander, Marleau, Kadri/ JVR, Bozak, Marner, (Brown, Komarov, or Kapanen?)
PK (need 4): Hyman, Komarov, Moore, (Brown or Kapanen?)
Because of this, there's no room for guys like Leivo or Soshnikov to make the team unless one or two guys on the PP get hurt (knock on wood). Neither of them plays PK and according to interviews last year, that was one of the biggest reasons why he wasn't able to play Leivo.
Unless Komarov or JVR are traded, it's gonna be a tough task to make the team.