The latest Canon 5Ds are specialized cameras mainly for landscape and studio photography. These cameras don't have a fast burst rate, and the RAW image from the 50MP would take lots of hard drive room once you have post processed and saved it to TIF format, or even DNG.
The 5D3 is now an older camera that will probably be replaced by a newer model (5D4) this year, but it has a fast burst rate which is desired for sports, wildlife, and fast moving subjects in addition to landscapes and studio photography. This is a well-rounded camera designed for general photography uses, not just a "specialized" one like the two above. You can put the 7D2 in this category, except that while the 5D has a full-frame sensor, the later has a cropped one.
What I did a few years ago was to keep my 7D and buy a 5D2. I use the 7D primarily for wildlife photography (birds, moose, etc.), and the occasional landscape and Northern lights shot. I use the 5D2 primarily for landscapes and Northern lights, portraits, and the occasional pets, and wildlife.
If I were you I would buy a 7D2, and three to four years from now buy a Canon refurbished 5D4, or maybe the "by then upgraded" 6D+
By the way, while you don't do fast sports photography, shooting birds benefits greatly from fast-shooting cameras such as the 5D3, and 7D series. Of course a 1DX would be even better, but it's just too expensive
No idea if this will work, but it is a PDF file that shows how to set the 7D2:
EOS_7D_Mark_II_AF-Setting_Guide-p9090-c3945-en_EU-1410782521.pdf
