Here's who I think will cameo in the next few episodes -
Grand Chef Auto - Duncan, only because whenever I see the title of this episode I think of him, because he's like a badboy and a criminal and stuff.
Up, Up And Away In My Pitiful Balloon - Most likely Heather. I know there is no explanation, but the other episodes below match those characters, and Heather is the only one who hasn't had a cameo prediction from me. So I just think she's in here.
Eat, Puke and Be Wary - I think DJ, because he's like a cook. Maybe he'll cook the food for the challenge or something.
The Enchanted Franken-Forest - Harold. Definitley. Because it seems like a "ninja" title to me. And Harold's like a ninja, right?
Now, for the last episode - I think none of the contestants will cameo, because Owen, Bridgette, Izzy, Gwen, Duncan, Heather, Lindsay, Harold, and DJ are the ones confirmed to appear, and unless Up, Up and Away doesn't have a cameo, then I'd have to say Heather will appear here, because she was the winner of the last season, TDWT.
I think the last episode will be called "A Million Dollar Diamond", because when I searched "Total Drama Revenge of the Island A Mine Is a Terrible Thing to Waste" on YouTube, one of the search results were "Total Drama Revenge of the Island A Million Dollar Diamond". Hmmm..... Well, that's my opinion. But also, a photo was leaked featuring Bridgette and Duncan wearing cowboy outfits about to battle. Maybe this is from Grand Chef Auto, because I mean maybe Bridgette is still an intern..maybe.