Starcraft – Which StarCraft units are not present in Wings of Liberty

Yes. Any achievement, any achievement, that has a difficulty requirement as part of the achievement can also be completed on a higher difficulty. This means that (if you're good enough) you can get all of the Wings of Liberty Mission achievements on a single playthrough.

E.g., for the Red Lobster achievement, you can taunt the Brutalisk into the lava on Normal, Hard, or Brutal -- you don't "have" to be on normal (despite the listing to the contrary)

In the starcraft 2 lore panels at blizzcon 2010 and 2011 they answered these questions. The canonical choices are the A choices, so

Raynor chose Tosh over Nova

Raynor chose Dr. Hanson over Selendis

Raynor chose the Tunnels in Belly of the Beast, not the platforms in Shatter the Sky

transcript for the first two.

Best I can find for the tunnels answer is the entire lore panel from 2011.