Arguably, the Leafs D corps organizational depth chart looks something like as follows, when counting defenders with some NHL experience: 

Morgan Rielly - Brandon Carlo

Jake McCabe - Chris Tanev

Simon Benoit - Oliver Ekman-Larsson

Henry Thrun - Philippe Myers

Dakota Mermis - Matt Benning

Marshall Rifai

With at least two more NHL contracted D men you would think the Leafs want to get a look at:

Cade Webber - William Villeneuve 

That's 13 NHL contracted defensemen and where depth on the blueline is vitally important, there is such a thing as a logjam. A situation where there is not enough ice time to go around, or legitimate NHLers are relegated to the minors having their path to the big club blocked by nothing other than the number of bodies. When this occurs it serves no one, neither the player or the team.

All of these players excepting Webber are waiver eligible, which is another factor. Injuries in other team's training camps could spark a waiver claim or two but I'm guessing that not every player listed here will be with the team in September. This looks to me like a situation where there will be issues satisfying the AHL veteran player rules. One part of these rules states: "That for each game an AHL team can only dress a maximum of five skaters that have played over 320 professional games."

Benning, Myers and Mermis would be considered as veterans under this rule. My point is that due to the large number of defenders, and with all things considered, that Brad Treliving will put together a deal which includes at least one of these players, possibly two of them.