Producer Johar is said to be keen to get the New York star on board after considering Deepika Padukone and Anushka Sharma, Mumbai Mirror reports.
Kaif and Kapoor dated for nearly 18 months, breaking up in April allegedly over rumours about Kapoor's reported involvement with Rockstar co-star Nargis Fakhri.
The couple met on the set of Prakash Jha's political drama Rajneeti but kept their romance under wraps to avoid media scrutiny.
A source told Mumbai Mirror: "She was very hurt after her break-up with Ranbir. After all, they were in a relationship for nearly 18 months. But all that is a thing of the past."
They added: "Katrina is totally focused on work now. She is back to being her usual happy and chirpy self. Life doesn't stop due to break-ups. Why shouldn't she work with Ranbir?"
However, the actress has still to sign a contract, despite unofficially taking on the lead.
According to the source, director Ayaan Mukerji had been waiting for Kaif to make up her mind after the two stars stopped dating.
The film will mark Kapoor and Kaif's third project together after Rajneeti and Ajab Prem Ki Gajab Kahaani.
Watch Katrina Kaif and Ranbir Kapoor in Rajneeti below: