Stage 3
Hiya ATC Hopeful,
If Stage 3 is just the same as what I had a few months ago, they will expect you to have a certain level of technical knowledge. This won't be because they sent you information which they expect you to learn, but because we were/are all expected to do independent research and fact-finding about ATC and the career. Just because there isn't a motivation paper doesn't mean you're not expected to show that you're motivated.
The Stage 2 document didn't have much influence on what knowledge I went into Stage 3 with. I read several books (Graham Duke's is a good introductory guide) and visited Prestwick Control (popped into Oceanic while I was there) and a tower, and spoke to a couple of ATCs I know as well as some other stuff.
If nothing had changed, expect scenario questions which may require some technical knowledge, perhaps some questions about the company and ATC operations as a whole, questions about your past and also a load of competency-based questions.
Good luck!