Feig just tweeted this
https://twitter.com/paulfeig/status/560178147954421760
Kristen Wiig as Ray Stantz
Melissa McCarthy as Slimer
Kate McKinnon as Peter Venkman
Leslie Jones as Winston Zeddemore
edit:
confirmed
https://twitter.com/paulfeig/status/560178147954421760
Kristen Wiig as Ray Stantz
Melissa McCarthy as Slimer
Kate McKinnon as Peter Venkman
Leslie Jones as Winston Zeddemore
in case you geniuses can't figure it out, they're not playing those roles.
edit:
confirmed