If you have Rokinon Cine lenses than why stick with Canon?
I had a t2i with Samyang (aka Rokinon) Cine lens and I moved over to the sony a7s. And honest I do not regret it one second. I have tried the 5d3 and sure its a great still camera. But if you do video and you have manual lens, the A7s is no brainer.
I can't talk for the c100 as I havent tried it but from a price point It is even cheaper than the two other options. You can find cheap NEX-EF adaptor since you don't need a smart one. Some even come with nd filters like the hollymanta.