This issue has driven me to distraction and I'm REALLY sick of people posting "solutions" that don't work, almost certainly because they're iPHONE users.
Irrespective of the "Reduce Motion" setting, or the "Perspective Zoom" setting, or whether the wallpaper dialogue is accessed directly through Settings or from within Photos, the outcome is always exactly the same for users of the iPAD models with retina resolution (2048 x 1536).
iOS 7 prioritizes PORTRAIT orientation (presumably because it is fundamentally designed to optimize the iPHONE interface, since that is Apple's cash cow product).
On the iPAD, as far as I can determine, a wallpaper image will NOT fit pixel-for-pixel in LANDSCAPE orientation, EVEN if the image is 2048 pixels SQUARE (or 2524 pixels for parallax).
iOS 7 will STILL, ALWAYS, zoom the landscape view up to the maximum width of the PORTRAIT screen (1536 native pixels - without parallax - or 1893 pixels with it).
I should publish a whole article on this nonsense in due course, with explanations, but in the meantime here is the fix that DOES work to get your wallpaper pixel-perfect on your iPad in landscape orientation.
A. Non-parallax ("Perspective Zoom" Off, "Reduce Motion" On):
1. Size your desired image to exactly 2048 pixels horizontal. Anything else is just stupid, no matter how big, because you want control over quality and only an exact pixel match between image and screen can ever achieve that.
2. Whatever the vertical size, crop it or add blank space ("canvas size") so that it's exactly 2731 pixels high.
3. Check: you now have a PORTRAIT image of 2048 x 2731 pixels.
4. Apply this as your wallpaper, zooming out for maximum viewable size. In landscape orientation, it will be a perfect fit. In portrait orientation, it will be reduced to fit, and any blank padding will be visible, but we don't care about that; only iPHONE users do, and Apple seems to like them much more than you and I.
B. Parallax ("Perspective Zoom"):
1. Size your desired image to exactly 2524 pixels horizontal. Again, anything else is just stupid, no matter how big, because you want control over quality and only an exact pixel match between image and screen can ever achieve that.
2. Whatever the vertical size, crop it or add blank space ("canvas size") so that it's exactly 3365 pixels high.
3. Check: you now have a PORTRAIT image of 2524 x 3365 pixels.
4. Apply this as your wallpaper. First turn Perspective Zoom Off, and zoom out completely for maximum viewable size. Now turn Perspective Zoom On: in landscape orientation, it will snap out to be a perfect pixel-for-pixel fit (as long as you don't tilt the iPad and move the image). This is as good as you can hope to get.