If the Braves traded Marte AND McCann, I'd be absoutely shocked. Not saying the Rays shouldn't demand that, but I have a hard time believing both would get shipped by the Braves.
Of the two, I can see Marte being the better possibility. With Chipper at 3rd for a few more years, and Betemit able to handle SS until Escobar is ready, with Betemit going to 3B, Marte could actually be argued to be a luxury unless they plan to play him in the OF.
However, watching a few Braves games, Estrada is not good defensively. I'm under the impression McCann is. If so, and based on the value the Braves place of defense and pitching, I think the Braves trade Estrada in the off-season - which means McCann likely isn't going anywhere.
Not to mention, I kind of like Toby Hall. He's not great, but he's solid, has a pretty good arm behind the plate and seems to call a good game (though I am by no means an expert there). I'd rather have the pitching help if I were the Rays.