Prior to the Canon EOS 5Ds announcement, several websites reported that the new 50MP sensor was developed with/by Sony. Apparently this is not the case - the sensor was developed and produced "completely in-house" by Canon. Here is the quote from Chuck Westfall:
Despite some rumors to the contrary, Westfall said the 50.6MP CMOS sensors in the 5DS and 5DS R are developed and produced by Canon. When asked whether they were created in collaboration with Sony as some rumors indicated, Westfall responded by saying: “Absolutely not. The sensors were developed completely in-house, by Canon.”
The new 50MP sensor offers no dynamic range improvements over the previous 5D Mark III sensor: