When he woke, he didn't have enough power to access his orb in order to use it. Solas probably didn't hand his orb over to Corypheus with some agreement, more likely he left it in a place for him to find in hopes that Cory would be able to generate enough power to unlock the orb for him. He expected Cory to die in the blast that destroyed Haven, where he would reclaim the orb fully activated and go on his way to finish his mission. That's... not what ended up happening. He's genuinely surprised by Cory's resilience and the fact that he survived. While he can theorize how, he doesn't know for sure because, unlike Flemythal, he's actually never had any experience dealing with blighted creatures. While he certainly knows soul jumping/body hopping is possible, I don't think he realized that humans figured out how to access it.
He recognizes his mistake and wants to get the orb back. He intends to use the Inquisitor/Inquisition to do the job for him.
Was he actually working with Corypheus? No. Was he using Corypheus to get what he wanted? Absolutely.
One of Solas' key failings is the fact that underneath all that unwashed apostate hobo he's a bit of a snob. A noble snob with similarities to both Vivienne and Dorian, actually. He just hides it better.