I really like the softer 2-syllable A names like
August.
Adair,
Avery, and
Allen also go very well. I'm not a huge fan of
Gabriel with this name because it feels awkward to say aloud.
My main advice is sticking to softer consonant sounds in the middle name because Whittaker can sound overly harsh with more sharp consonants in the rest of the name.
"Where words fail, music speaks." -Hans Christian Anderson