I went to school with a Sunny who's middle name was Brooke. I always thought it was a very pretty name.
Sunny Brooke
Sunny Jane
Sunny Jade
Sunny Paloma
Sunny Alexandra
Sunny Alyssa
Sunny Genevieve
Sunny Geneva
Sunny Kate
Sunny Catherine
Sunny Caitlin
Sunny Peyton
Sunny Leila
Sunny Mariah
Sunny Elise
Sunny Eliza
Sunny Elizabeth
Sunny Isobel
Sunny Isabella
Sunny Maeve
Sunny Matilda
Sunny Penelope
Sunny Athena
Sunny Artemis
Sunny Agnes
Sunny Agatha
Sunny Dionne
Sunny Magdalena
Cleo (I've never met a Cleo in person, but here's my suggestions):
Cleo Jane
Cleo Jade
Cleo Charlotte
Cleo Penelope
Cleo Artemis
Cleo Grace
Cleo June
Cleo Rain
Cleo Samantha
Cleo Savannah
Cleo Alexandria
Cleo Madeline
Cleo Matilda
Cleo Maisie
Cleo Brooklyn
Cleo Agatha
Cleo Agnes
Cleo Arianna
Cleo Daphne
Cleo Ivy
Cleo Margaret
I think both of these names actually share a lot of middle names that sound good with either name. So I repeated some, but feel free to mix and match. I tried to find some Greek middle names since Celena is also Greek.