The Linebreaker spell from the ARG states that, "You gain a +20 foot bonus to your base speed when charging and a +2 bonus on combat maneuver checks made to bull rush or overrun."
Questions:
1. Does the +20 ft bonus to base speed mean I am now gaining a +40 ft bonus on a charge? That wouldn't seem to be the intent, but not sure how to read it.
2. I assume this will stack with spells like Haste or Expeditious Retreat since it's an untyped bonus. Is this correct?
Yes to both.
1) You go twice your speed = 2 x (base speed + enhancement + whatever else)
2) It's an unnamed bonus to speed, which will stack with Haste or Expeditious Retreat which are enhancement bonuses.