That lineup is 294,800 under the cap. Dermott and Mikheyev are still unsigned. You could probably trade Johnsson (3.4M) and have 3.7M to get those two signed and then depending on left-overs have enough to sign about a million dollar player but the Leafs would be dressing a lineup with no healthy scratches that way. You could also trade Dermott at this point because he's going to get exposed in the expansion draft next year.
With Johnsson dealt and Mikheyev and Dermott signing $1.5mil and $1mil deals this roster gives us just under $500k in space:
Hyman-Matthews-Nylander
Mikheyev-Tavares-Marner
Robertson-Kerfoot-Simmonds
Engvall-Spezza-Barabanov
Rielly-Brodie
Muzzin-Holl
Dermott-Lehtonen
Marincin
Andersen
Campbell
21 man roster so we'll be able to carry 1 extra player. I picked Marincin because he rules and has the lowest cap among the other defenceman so we'll accrue more cap space during the season with him. He could also get yo-yo'd if he clears waivers (and the AHL is a thing) when need be.
I mentioned Thornton and Koviu as other forwards I was interested in. We could squeeze Thornton in if we dealt Engvall and Koivu if we sent Barabanov to the minors assuming they were ok with $1.5mil and $1mil deals. edit: that would actually put us a whole $36k over so take $50k off of Dermott's AAV just to be safe.