The question about uploading but not activating is not something that I can answer. I doubt that any of the agencies would want to do that. They wouldn't want to waste time reviewing something they can't sell, I would think. Why would you even need to do this? Either you're exclusive or you aren't.
Pond5, Shutterstock and Revostock are excellent. Never made a sale at clipcanvas, and don't bother wasting the bandwidth there anymore.
Don't touch FT with a ten foot pole- they pay very little, the reviewers are incompetent, and they are in one of their periodic cycles of finding new ways to screw the contributors.
The smaller site- AlwaysHD, etc, are not worth the time.
Hope this helps.