I was announced this weekend at the New York Comic Con that the two-issue crossover will happen in Spring and will take place in UNBEATABLE SQUIRREL GIRL #6 and HOWARD THE DUCK #6!
The story appears to have a cosplay theme happening, given the convention setting, the Spider-Man suggestion for cosplaying as him, as well as the image of Howard and Doreen wearing outfits normally worn by the other. But that's just speculation!