Recently dropped in the Starcraft 2 Campeign Q&A:

Choices that you make in Wings of Liberty will be persistant in Heart of the Swarm in the plot – this means that if you decided to kill Dr. Hanson for example, she'll stay dead. There is no default answer that's considered "canon" as long as you played through Wings of Liberty. If you did not play through the original game, all of the choices default to the first choice, or "A" as the devs called it.

More from Blizzcon as it develops.