Big Time Spoilers
I am not saying any of this is official, but here you go:
"Cinema Blend has news that Theresa Russell is in the cast as the character Felicia Hardy. You a Spidey comic fan? That mean anything to you? Let me elucidate.....
According to Comic Book Resources, Russell's character will carry the name Felicia Hardy, and all the weight that goes with that. To those who know Spidey lore, Hardy fell in love with Spider-Man and made an agreement with the Kingpin that gave her super powers (under the name Black Cat) so she could hold her own with Spider-Man. The two were romantically involved until Peter Parker chose to leave the Black Cat for Mary Jane Watson."
This came from a reliable person that is involved with the production of Spiderman 3...
Here is something about Harry :
(CAUTION Spoilers ahead)
Rob, all the assumptions that Harry Osborn is the third villain the Hobgoblin are all wrong. Spiderman finds himself out numbered in this one. When everything seems to be at its worst for our hero, he finds himself an unlikely ally, Harry Osborn. Peter Parker's best friend will come to his aide.
Okay so let's look at this. Harry will come to Spidey's rescue? Did he finally realize his father was a kook? Apparently so. Here's more...
We will see Harry battling his inner demons to make the choice between his father's legacy and his best friend. I will fill you in more later but gotta go, crew call in 10 minutes, Sam doesn't like it when anyones late!
Source : themovieblog.com