This came up on the BGG forums, and I realised I wasn't sure of the answer.
Visionary uses her one shot to look at the top 3 cards of the villain deck.
1. If one of those three cards is a trap, does it go off?
2. If the fourth card (now visible on top of the deck while Visionary makes a decision) is a trap, does it go off, even though Visionary will be putting a card back on top of it?
For 1, I'm pretty sure the answer is yes, the trap goes off and you draw a replacement.
For 2, I hadn't considered it, but I would suggest that yes, it does go off as it is on top of the deck. Which makes Ambuscade more dangerous for Visionary as it only has to be in the top 4 cards to trigger.
The answers are both yes. Somewhere on the forums there's a discussion on Wraith's eyepiece and the same situation, it was ruled BOOM!
In fact, it was ruled that the sequence would be something like this:
1) Pick up first card for viewing.
2) Notice that next card is a trap. Stop and fully resolve the trap.
3) Pick up second card for viewing and then proceed as normal (unless the card under is also a trap).
I mention this only because it's important to note that you stop resolving Eyepiece (or whatever) and resolve the trap, and then continue. This could result in A) Wraith dying because of the trap, in which case, I believe the Eyepiece stops, or B) Perhaps in some edge case that what the Trap does affects your decision of what card to put on top.
Which brings up the question of what happens to the revealed cards if wraith dies and eyepiece stops working. The whole idea of the traps going off is based on the idea that the cards are temporarily pulled off the deck, so I guess I would put them in the trash?