Given their cap situation and need for a forward or two, Ducks should consider offers for any defensemen not named Lindholm. Prior to the season, I thought Fowler was the best trade option, but given how well he's played, I have reconsidered. I'd rather trade Vatanen, but that would be hard since he just signed.
But in any trade made at this point of the season, the ducks need to be a better team THIS year. That means the trade needs to bring back an affordable top level forward or two who can contribute immediately. Kapenen is a nice prospect, but there is no reason to trade Fowler for him given those paramaters. If the ducks want to trade for Kapenen (or a player like him), they'd be better off trading Vats or one of their defensive prospects.
If the ducks fall out of contention, then at the deadline they can revisit the return in a trade or trades. But in any event, I think Fowler gets more at the deadline than Kapenen. Any team trading form him gets him for two playoff runs.