The Leafs need to find a way to shed about $500k in cap to be able to bring Ritchie, or a theoretical replacement upgrade forward, off the taxi-squad.
Travis Dermott, who's being used interchangeably with Sandin & Liljegren at $1.5m would be a very logical place to do it. Additionally, I'd imagine that the Leafs do want to replace Bogosian, and get somebody with a little bit of toughness that can be inserted into the lineup.
That being said, I think there are too many moving pieces in these 2 deals. With Holl, there's a lot to like about his fit with Sandin on a #3 pair, and he has shown great chemistry in the past with Muzzin on a #2 pair.
They'd probably be looking to swap out 1 defenceman -- with the guy going out being Dermott, and the guy coming in being somebody like Schenn, Braun, Bortuzzo, Mayfield.... not because these guys are better defencemen, but because these guys bring elements to their game that the Leafs blueline doesn't really have an abundance of.
In order of preference, I'd imagine that it would go Mayfield, Braun (assuming salary retention), Schenn, Bortuzzo; but can certainly see Schenn jumping Braun if Philly isn't willing to retain on Braun.