At the start of The Witcher 3 - The Wild Hunt you can either

import a savegame (PC only)
select the decisions you made in Witcher 2 (Simulate Witcher 2 Decisions)
skip the whole import of decisions
If you chose to select the decisions (or import a savegame) there are 5 major decisions which will have some kind of impact on the game.

Care: The Witcher 2 - Assassin of Kings Spoilers ahead

These decisions depend on if you:

killed or spared Aryan LaValette
sided with Iorveth or Roche
saved Triss or saved Saskia/Anais
saved Sile de Tancarville or let her die
killed or spared Letho
If you chose not to import any of your decisions, what will be the (supposedly default/canon) world-state regarding these decisions?

Just to clarify things: I'm not asking about the actual impact of decisions, I just want to know, what the game assumes on default if you don't import any decisions.

Default world states as I understand them, based on actual play-through:

* - Sided with Roche
* - There is no hangover tattoo
* - Letho is killed
* - Triss is saved
* - Sile is killed (not in TW3 prison)
* - Anais in exile (Roche)
* - Henselt killed
* - Aryan La Valette killed
* - Saskia's fate unknown

Wanted to add that Henselt is dead no matter what. If you import a save where you didn't kill Henselt, Henselt is still dead before W3 under different circumstances (killed in battle I believe), Everything else is right on as far as I remember.