Flood's character Josh Ashworth is back on screen for two episodes next week after nearly two years away from the show.
Viewers will see Slanina-Davies's alter ego Amy Barnes receive comfort and advice from Josh after her relationship with Ally Grogan hits the rocks.
"It's a huge surprise for Amy to see Josh again, but she's really excited about it," Slanina-Davies told All About Soap. "They've not seen each other for a long while, so they've got a lot of catching up to do."
She continued: "As far as I'm aware, it's just a small guest appearance, but I'd love to see Sonny come back for good. It was so good getting to work with him again - it felt like no time had passed."
The actress also revealed that life has changed for the better for Josh since his departure from the village.
She said: "He's got engaged to this really amazing girl. Josh has a picture of his fiancée and she's the most beautiful woman with a perfect figure. Josh has joined his dream music course and he's got his own flat, which makes Amy feel a bit rubbish about her own life in comparison."
Hollyoaks airs weeknights at 6.30pm on Channel 4, with a first look screening at 7pm on E4.