Couple thoughts from a Canes fan:
Regardless of players involved, any Canes trade for Nylander would obviously first require that he agree to a contract the Canes consider "reasonable" (which could be more than what Leafs are offering). Canes can't significantly overpay Nylander because of the effect it would have on negotiations with the current players they'll need to re-sign next year.
An offer sheet from the Canes doesn't make much sense imo. Just on principle, the Leafs would match more on an offer sheet than they'd be willing to offer Nylander without one. So unless it's a significant overpayment, which the Canes can't do, all an offer sheet does for the Canes is make cap issues slightly tougher for the Leafs (not even a Division foe), and create a grudge.
Necas isn't going to be a plus in any package from the Canes (unless it's for Matthews, which obviously isn't going to happen). Anyone suggesting otherwise clearly has no clue about the Canes organization.
Pesce's contract does increase his value. Another team signing Nylander will likely require at least a slight "overpayment", which doesn't help his. Even taking that into account, I don't see the Leafs adding in a Nylander <--> Pesce trade. Canes might add, but I don't see it as being very much.