Actually I think the best solution is to trade Pulock plus Wahlstrom to Canucks for Boeser which I think will be win-win. Boeser has even better shots than Laine and he is a competitor and already knows Nelson well. Canucks will bite because Pulock will be the perfect partner Hughes needs and Wahlstrom can potentially replace Boeser down the road. If this is too much for Isles, Canucks has some pretty good prospects in the system and Isles can maybe ask for one of them coming back. Getting Boeser may be the key to entice Barzal to stay with Isles too. Wahlstrom will be the trigger that will pull the trade.
To resign both Barzal and Boeser, you will have to move another contract, thus trade Cizikas to a western team missing a top defensive center capable to fit him under their cap. Maybe the Oilers be interested? He can be the difference helping them to make the postseason and do well in the playoff. Leddy will have to go too to make room for resigning Beau, Toews, and Pelech. Just find a team that needs an LD and has the cap room to add him. Go with the highest bidder for him, but only take picks/prospects coming back. Resign Greene for a year with Aho as the first injury call up a replacement. Dobson into Pulock's spot with BJ and Mayfield taking turns on 4th and 6th spot. Send a college RD or Wilde to AHL to prep for RD call up for injury replacement.
By the way, do not downplay Reinhart that much. Even you go to the Sabres board they actually really like him and would not give him away easily. He was picked #2 overall for a reason and may not yet fully fulfill his elite potential yet.
Now about how to find that sniper for Barzal? You will have to overpay a UFA and may not have room anyway and you do not have high enough draft this year to get one via the draft and the best asset you can potentially move to land one is probably Pulock so do the math. If you can resign Barzal via a short bridge deal you better find that sniper within one year or he will not come back next time. If any team has a sniper already they will either hold on to him or demand a random coming back via a trade - top D, top prospect, and draft pick. Or maybe you will get an older winger with an expansive expiring contract who was a sniper but has lost that consistency due to aging/injury (like Perry and Ladd). The only other option is to keep one of Wahlstrom and Bellows and hope they can turn into a 30 + goal scorers or make a deal like Pulock + for Boeser (both RFA and both team has different top needs).
Of course, the best option for Isles is:
1) trade Leddy and Cizikas for cap space in the fall
2) resign Barzal and Pulock assuming no crazy offer sheet out there to distract either one of them to get it done before next season start
3) do not bring Martin back, get Johnston to play for his spot or another LW prospect
4) trade another asset to hopefully get a prospect who can score goals or a player who did before but has for some reason not yet kept up that lately to help with depth scoring (Comtois or Milano from Anaheim and Mantha from Detroit hopefully maybe trade options without too much going back the other way)
5) Promote one of Bellows, Wahlstrom, or Homestrom for a chance to play with the team on bottom lines first, priority to Bellows if not traded in any package
6) promote Otto to play 4th line center for Isles
Other options are out there as some may have suggested with Parise and so on. I still think Ladd's contract will be really hard to move unless you add a big sweetener with it so there will be a big cost to this. If you can find a way to trade Komarov for the bottom 2020 pick you do it too.