Difference between 你能看完这本书吗？ vs 你看得完这本书吗？
I think basically what you wrote in your question is right. 

As for: 


  What's the difference between 你能看完这本书吗？and 你看得完这本书吗?


Let's remove 这本书. 你能看完吗？vs 你看得完吗?, I can't seize any difference in meaning between them. It's just different syntax being used to express the same semantics. In practice, you can probably replace one with the other without any problems.