He legit should have been Conrad Verner.

Conrad is this goofball Shepard doesn't take serious, but what if he was a Cerberus plant to learn more about Shep and the Alliance/Spectre's?

Gaining Shep's trust allows him to have the upper hand in ME3 because he knows how you operate, which is why he's always one step ahead of you. It would also make Thessia have a much cooler impact and fight because this is someone Shep and the players considered a friend. The loss would feel earned. Thessia would also be where he'd reveal who he is.

After Shep defies Cerberus in ME2, that sets the events with them in motion for ME3, which makes Conrad an active player towards Shep now.

It just makes too much sense! Conrad could have been way more cool.