Id be surprised if Whitfield didn't play down back, especially with their lack of experience in defence right now, it's essentially a bunch of kids running the ball out of the back half.
To be fair the two kids doing most of the work are very high draft picks with bright futures in the roles so I don't expect them to mess with it. I think Whitfield, assuming he's fit, will play as a roaming wing as he mostly has the past couple of years, they need him as a target up the field more than a rebounder and him kicking towards the forward half instead of the likes of Hopper, Ward and Taranto would make a massive difference to their overall ball movement.
Giants aren't really doing a lot of sensible things with their selections though right now. Their best midfielder is playing forward, their best intercept defender is on a wing, their best small forward is playing midfield, they're playing their ruck coach instead of developing their future ruck stocks and it goes on.
Personally expect that Whitfield will replace Stone in the side and rolewise. He's just going to be a lot better at this stage in the role.
Is Jake Lever an option for Howe?
Yes but I'm not sure he's not an unnecessary level of risk, he's extremely unique and May has been out the last couple of weeks who will impact him to a degree at least and it's worth noting that Melbourne haven't faced any really decent sides, especially in the forwards stakes, and that the only side that even "kind of" has two KPFs he scored 53 against. Freo and the Hawks literally looked like they were kicking to him, GWS don't even have a KPF to the point that an undersized midfielder is their main marking target and a 175cm jockey sized guy is their secondary target and Geelong are so one dimensional that he just stood in front of Hawkins and intercepted all day.
Having thrown the negatives, he's still scoring great and unique can be good as long as it works. To be honest though it reminds me of a few years back when Tom Jonas was a legitimate premium for half the season before they started to face some stronger sides and he got stuck in non-favourable matchups where he had to defend more and his scoring fell back more towards what the role generally scores. Reckon he's a 90 type more likely than a 100 type but if you feel strongly about him you should back it in.