Not wanting to invest in a new set of lenses for my Sony A7R, I have been considering using an adapter to allow me to use my Canon lenses with A7R. I have been looking at online reviews of various available adapters and settled on the Commlite CM-EF-NEX adapter (http://www.amazon.com/gp/product/B00J3MFI3K/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 ), the same adapter that Serge Ramelli uses. It seemed to have more favorable reviews than a better known Metabones adapter and at a several fold lower price. Thus far, I only had an opportunity to evaluate it very briefly with my Canon 17-40 and 70-200 F/4 L lenses and it seems to work well. It allows me to control autofocus and f stop controls and the image quality seems fine. Couple days ago,Blake Rudis posted a favorable review of Fotga adapter (http://everydayhdr.com/fotga-canon-to-sony-e-mount-review/ ) which also does an acceptable job for joining Canon lenses with Sony cameras. I will post more on my evaluation of the Commlite adapter as I start using it more.
The other reason for wanting to use my Canon lenses was a relative lack of available lenses for Sony full frame cameras. However, one drawback of using Canon lenses with Sony cameras is the size and weight of Canon lenses. This somewhat defeats the purpose of having a light and small camera. On the other hand, some of Sony lenses designed for their cameras are of comparable weight and size to Canon's. For example, Sony 70-200 F/4 lens is slightly larger and heavier than Canon 70-200 F/4 lens.