Then what about next year when Barzal, Pulock and Toews become RFA's? That's going to require $20,000,000 cap space.

That costs wwwaaayyy too much. We'd be helping them out here. Better off just signing him on an Offer Sheet and giving up the 4 1st Round Picks.

$20,000,000 is far higher than it needs to be

If you look at the long term outlook there will be approx 13 mil in cap space to re-sign the 3 RFA's and sign or replace 3 UFA's. Barzal is going to be 6-7 million, Pulock and Toews 5-6 million at least, so yeah with replacing the UFA's as well it's going to take at least 20 million of cap space next year. I'm guessing you want to stick it to Toronto by signing Marner, but the best way to stick it to Toronto is to not be Toronto.