And while Canon is criticized for "refusing" to deliver more DR, it is Nikon and Sony that are failing to deliver video performance to match that of the 5D3.
Which is why you keep your 5D3 for sports and video and buy the A7R for your landscapes. If Canon were update to date with sensors you'd just buy the one Canon but they aren't so you add the A7R.
(also 5D3 only rules for video mostly because of the ML hack, so while Canon engineers did make a camera that delivers video in spades, marketing or someone had it shipped pretty crippled; it is surprising that Sony punts so badly on video though I will add, if anyone should have that down it should be them).
The A7R will be great for landscapes, and will no doubt provide more detail for very large prints. However, you don't need an A7R for landscapes. Starting in 2008, Salgado used the previous generation 1DS3 to photograph landscapes and other subjects in Algeria, Alaska, Arizona, Brazil, etc. The result is a magnificent book. As early as 2002, Michael Reichmann (Luminous-Landscape.com) favored the original 1DS over the medium format Pentax 67II. So Canon sensors have been up to the task of landscape photography for quite some time. DR is just one of many factors in choosing a landscape camera.
The Camera labs review (http://www.cameralabs.com/reviews/Sony_Alpha_A7r/) of the A7 & A7R is pretty clear on the 5D3 having superior video quality. No Magic Lantern is involved in that conclusion.