Structurally, this trade won't work because Seattle isn't trading anything to San Jose for Kane. For retention trades, there has to be something going the other way and it essentially has to function as two separate trades.
If the Sharks are trading with Seattle to move Kane and giving them a 2nd, Seattle will need to send San Jose back something then send Kane along at 50% to Edmonton for whatever. A Kane deal to anywhere to where the receiving team is going to get him at 25% of his cap hit is not going to include all of this.
The odds that a deal is there to be made where a team gets Kane at 25% is unlikely considering the circumstances. With three seasons to go after this one, it's difficult to ask a third team to eat 1.75 mil in dead cap for that long let alone gauge a good value for it. I think the conversation needs to steer more towards which teams will want Kane at 3.5 mil while also having a similar term contract to send back as the basis for a trade. If things don't work out for that team, the buyout is only 50% on you. That sort of cap hit is 1.8, 1.3, 2.3, and 833k for three more seasons. This assumes that things go south quickly with Kane which seems unlikely. Kane doesn't tend to wear out his welcome until his third or fourth year.
The risk that is there with what is laid out can be determined if it's worth it or not by each individual but it seems super unlikely any of these double retention trades will materialize. The Sharks will buy him out if the cost to move him is really anything beyond retention plus a 3.5 mil contract returned or players they don't value moving forward. Those players likely not being anything anyone else would want to trade for anyway.
