If you are on a mountain, then you get a significant bonus, +2 (though the bonus is less significant if the attacker is also on a mountain, being +1 then, as they're not fighting uphill).Of the choices above, the Maryland Campaign looks to me like the more straight forward of the group.
Does terrain play any part, such as does heading for high ground get you an advantage.?
If you're defending a river crossing you get a significant bonus. (+2)
Defending a creek gives you a smaller bonus (+1).
High ground and rivers also make it much harder for the enemy to outflank you, though, which is actually the more important benefit in many cases. Outflanking can give up to a +4 bonus if a unit is completely surrounded. (Flanking units don't have to actually launch attacks to gain the benefit, pressure on the flanks is enough to grant the bonus.)
There's often a defensive advantage to flatter terrain, though. Flat terrain means that artillery can work better, and equal numbers of batteries on both sides mean the defender has an advantage.
This means that effectively the ideal defensive position is clear ground behind a significant river crossing.