Ok, so he essentially did a plea bargain. The DUI is still going to show up on a CIC background check and you will STILL need to answer for it. It wouldn't show up on a FBI sheet anyhow as it's not a federal offense. I would go ahead and get a state clearance for him as well and take a look and see what it says. That is where this record would be. Even if that clearance comes up clean, you are still going to have to tell CIC about his DUI arrest and such. Obviously he has done what was required of him and such, it's a matter of how Canada will treat this offense now.
How long ago did this happen? I am still thinking he might have to file for criminal rehab, but I might be totally off base on this. As I said, it will still have to be listed in the part of his application where it asks if you have ever been arrested or convicted of a crime, blah blah blah and asks for details in regards to that. As soon as he checks "yes" and answers it was for DUI that is where the problem will occur. Even though he pled out and did other things to have it 'expunged' I am willing to bet it is still there and even if he doesn't mention it and then CIC finds it they will accuse him of misrepresentation and that will throw a whole NEW wrench into your ballgame. One that you don't even want to begin to deal with.
The big question is whether or not to file for criminal rehab or not based on what shows up.
I really would get his state PCC and see what it shows. If it shows nothing, then I would go ahead and file regular sponsorship paperwork. I would note what I was arrested for and such then attach a separate explanation sheet stating EXACTLY what happened, what was pled, what the penalty was and what the results of it all was. Attach court documents if he has them or if he had a lawyer, ask them for case file on it. Attach it ALL. If CIC then still requires a criminal rehab I would think they will ask for it. If they accept his explanation and his attached files (photocopies should be fine) then they will continue the process as normal. Just make sure you absolutely disclose it even if it doesn't show up anywhere. Do NOT risk a misrepresentation label.