Who will be on The Invaders? Johnston wouldn't say, but here are some possibilities, based on the comics:

The Human Torch. No, not that one. The original Human Torch was an android who appeared in Marvel Comics #1 in 1939. At Comic Con Feige confirmed that while Fox owned the Johnny Storm Human Torch from Fantastic Four, Marvel Studios retained the android Torch. And in fact Feige used the android Torch as a way of explaining why the Marvel Universe's WWII is so distinct. Don't be too surprised if the Torch shows up. He had a sidekick named Toro, who had the exact same powers as the Torch. It may be possible that Marvel uses the Toro name to avoid confusion with the Fantastic Four character (and to make the Torch Spanish), but I think it would be great to spit in Fox's eye and use the original Human Torch.

Union Jack. I'd more or less bet money on him being on the team. In the comics, Union Jack is an older adventurer who was active in WWI. He had no superpowers but wore a bulletproof outfit and was exceptionally athletic.

Spitfire. Union Jack's daughter, Spitfire can run at superfast speeds, leaving a trail of fire behind her.

Blazing Skull. A really weird character, Blazing Skull is a guy who trained with Chinese  monks and has superhuman strength and can make his tissue - just his skin and muscles! - invisible, leaving the appearance of a walking skeleton. He wears a flaming skull mask. The Blazing Skull was an American in the comics, but could easily be made into a Chinese character. The only downside is that visually he's identical to Ghost Rider.

Silver Scorpion. Another American who could be changed into a European. A woman who is a jiu-jitsu master, Silver Scorpion had a sting-ray built into her suit. Despite being called the Silver Scorpion she had a yellow costume with a red cape and blue boots. A massive redesign would be needed.

European Defense Initiative. It's also possible that the film will go with a concept floated in The Ultimates, the EDI. Although set in the modern day and not in WWII, EDI is made up of heroes from multiple European countries, with characters like Captain Italy, Captain Spain, etc. To me this would be a cheap and easy cop out, though, and if The Invaders are important in the second half of The First Avenger: Captain America, it would make more sense to create full characters for them rather than simple Captain America knock-offs.

Namor, The Sub-Mariner. Incredibly unlikely, but possible. Fox, holder of the Fantastic Four characters, has Namor, but might that just be the Silver Age version? Namor actually first appeared in Marvel Comics #1, in the same issue as the android Human Torch. He was a founding member of The Invaders (which was actually called The All-Winners Squad back in the 40s), so he really belongs on the team. Of course even if Marvel does own the Golden Age version of Namor (which is essentially exactly the same as the Silver Age version), they may not want to confuse matters by using him in The First Avenger: Captain America while he might yet turn up in a rebooted Fantastic Four or his own film.

Others. There's a whole host of WWII characters that could be used, from The Thin Man - one of the first stretching superheros, beating Plastic Man to the punch - to the Blue Bullet - a Polish Jew. It's possible that the film could dip into this massive, mostly untapped well of characters and really surprise us.

Some guy in Edinburgh is loitering around the set of John Landis' new film Burke & Hare, and apparently he's made friends with some members of the crew. My guess is that he's met a PA or two, because nobody higher up on the food chain than a traffic wrangler is going to risk his position making buddies with a dude who is standing around the shoot taking pictures all the time. Anyway, this guy hears from his friend that Marvel is delaying The First Avenger: Captain America and they're doing it so they can replace Joe Johnston as director, thanks to The Wolfman not doing well.

I don't think this is true, and even if it is true, I still don't think it's true. Let me explain.

First of all, Johnston's essentially blame-free on The Wolfman. Everybody knows he walked into a movie that was to start shooting two weeks from his hire date. While The Wolfman is pretty much a disaster at this point, Johnston is at the very least insulated. And I have to imagine that when Marvel was making their deal with Johnston the spectre of that movie tanking was very obvious (and probably allowed Marvel to get a better deal out of him). But on top of that, Johnston signed a deal. They can't just fire him because they don't like his last movie's box office. They'd need another reason.

If the movie is being delayed and if it's because they're replacing Johnston the reason that makes more sense is that he's being a pain in the butt with Marvel. It's been reported that Johnston has fought with them about the budget of the movie, going so far as to threaten to walk. Maybe Marvel let him do just that after another round of budget battles.

What seems more likely to me is that the PA who is feeding this guy info is in on the local film industry gossip loop. You have to be if you want to work in film; you have to be up on what's coming and who's doing it and what they need. So this PA is in this loop and there are rumors that start, perhaps being sparked by the fact that Johnston did threaten to walk from Captain America some time in the recent past.

I don't know. It's also possible that the film is getting delayed for other reasons, like trying to work out a schedule with a star (there are a couple of Cap candidates who weren't on that leaked list the other day because their schedules wouldn't permit them to come aboard; could Marvel have decided to get the right guy as opposed to hitting a date? Very possible with these folks). And it's possible that the movie isn't delayed at all.

I put in a call to Marvel Studios and got nothing, so I'll leave this one to folks with better contacts on the inside than what I have. This is a production that's got a lot going on with it. Casting Cap is potentially too important to be left to a hard deadline, I've heard that the script really needs some serious work and Johnston has been battling the studio for every nickel and dime he can get. A delay isn't beyond belief, but until it comes from a more reliable source I'm not going to assume it's the case.