What are the issues with where the TV is now? Before you mount the TV over the fireplace, make sure that you have a comfortable viewing angle from the sectional. If the TV is too high or the sofa isn't in a good place, you may have to tilt your head up to watch TV--if you are watching a long movie, that can get tiring. I kind of like the TV where it is now. You have a "focal wall" instead of a focal point, so to speak. Depending on the amount of room in that corner, I'd look for a corner TV stand that would make the best use of the space. Right now, with the TV in the corner, everyone sitting on the sectional has a decent view of the screen. If you keep the sectional where it is and mount the TV over the fireplace, at least half of the sectional will be at right angles to the screen and people sitting there would have to turn their heads awkwardly to see it. Not an issue if you only ever have two people watching TV at a time. More of an issue if several people use that room to watch TV on a daily basis.

I would think carefully about a large U sectional. You might want to find the exact dimensions of one you are considering and mark it out on your floor. I'm guessing it will block the view out your french doors and be too close to them. If you want layout help you should post a floor plan with dimensions, showing all the openings, door, windows, etc. How do you want to use the room? How many people? What are the adjoining rooms and walkways?

How large of a tv will you have? What type of seating (sectional, sofa, etc.)? Putting it it in the corner will take up far more floor space than putting it against a straight wall. I'd be more inclined to put it on the Bedroom 2 long wall so that you could do a wall unit. To leave your options option, could you have it run to both locations but have them to where they could be easily hidden if not used?

You could always design a TV cabinet about the size of a console table. Then put the TV inside with the ability to raise it up to the top of the console when in use. Arrange the room to fit the console where you so desire it. Second choice would be to put it in one of those two wall display/book cabinets.