Just do what iv done and make the game in portrait and rotate everything to landscape by render to a back buffer then rotate and render to screen.
then in your Intiialize()
//the size of the backbuffer
BackBuffer = new RenderTarget2D(GraphicsDevice, 1280, 720);
Then in your draw
//enter your draw code here
gameBatch.Draw(BackBuffer, new Vector2(360, 640), null, Color.White, MathHelper.PiOver2, new Vector2(640,360), 1f, SpriteEffects.None, 0f);
MathHelper.PiOver2 will rotate one way and -MathHelper.PiOver2 will rotate the other way
you just need to work out the touch points as the will still report in portrait mode.
Of course you will need to handle the different size of screens, this code is only for 1280x720 as I haven't got round to auto scaling for all screen sizes.
Use the above code provided by Fox9 to make the game run in portrait mode.