I have a Canon 5D and I would like to connect it to a 720p monitor/tv as a preview for my client as I'm taking still images. I've had success connecting my camera via HDMI when I'm recording video, but not for still photography. The connection does not have to be HDMI, I'm open to any and all suggestions.
My 5Dmkii is with my partner on a shoot, but I don't see an issue. If it's in live view it should display what you're seeing with some blackout while the still is being recorded.
Alternately, why not tether via usb to a laptop with lightroom or EOS utility? Both programs can tether and display what lands in a watch folder.
As a fair warning, on-set client review will slow down your day tremendously if you aren't use to it. Not to say that all clients are horrible, but the general talking-over of numerous shots eats time quite a bit.