Engvall might clear waivers and would probably be my choice as well if someone had to be sent down.
However, replacing him with a wildcard like Kane is a high-risk, high-reward gambit that might work, but could leave the roster in worse shape after all is said and done.
If another player – such as Engvall – were lost on waivers and if Kane didn't work out, then the Leafs would have lost a roster player, which is not at all helpful.
There would be less risk if the Leafs weren't so close to the salary-cap and could carry a full 23-man roster. This is one of the consequences of leaving little flexibility on the roster.
If I were the decision-maker, I'm not at all sure that I would be willing to risk much on signing Evander Kane.