With only 1 retention slot, it's tough to figure out who to use it on because ideally you'd want to move - Rust, Rakell, Pettersson and if you're "able to" - Nedeljkovic and Grzelcyk and then the "if you pray hard enough for a miracle" - Jarry and Graves.
Rakell wouldn't be hard to move but his cap hit might be without retention, you'd likely be fine taking back a bad contract with 1-2yrs left on it at worst.
Rust I think is tougher of the two but he has playoff pedigree that might interest teams enough as well as his pk ability, he's a 125k more cap hit than Rakell, likely similar situation, taking a bad contract back with 1-2yrs left on it. Both can bring back a pick and a prospect I think.
Pettersson I think you would be better using the retention on, pending UFA, eating salary would get a bigger return and he's going to be a coveted asset at 30-50% retention.
I think Ned and Grz you'd maybe be stuck with Ned but Grz might be someone Boston buys low on to get back to to pair with McAvoy if they're still intending to battle for a spot and do up until the deadline, maybe a deal of Grzelcyk + Pens 4th '25 for Peeke + Boston's 3rd next season. Peeke has another year left, both cap hits are a wash.
I think the Canucks might pull the trigger on the Marcus Pettersson deal in the next day or so. I'd be shocked if JR/Allvin haven't added Marcus before end of day Thursday. Definitely a cap dump heading back with that one.