No, for three reasons:
First, Rapier specifically states:
You can’t wield a rapier in two hands in order to apply 1½ times your Strength bonus to damage.
Second, Weapon Finesse allows you to use DEX mod instead of STR mod on attack rolls. Wielding a one handed weapon in two hands allows you to add to your damage rolls. Two completely different cases.
Third, you cannot use Weapon Finesse when wielding two handed weapons, or wielding a one handed weapon in two hands. There are a couple of specific items that change this ( iirc, Elven Courtblade from Races of the Wild and the cheesechain Spiked Chain ), but it is limited to those items.
It is actually possible for a space marine to dual wield two-handed weapons, though a DM might not allow it.
In BC, space marines are automatically ambidextrous. And, as a space marine, you can take a power armor mod called 'Recoil Suppression' that lets you use Basic weapons one handed without the penalty.1
Slap on the Two Weapon Fighter (Ranged) talent, and you're good to go. Although any shots are going to be at a -10 for both weapons. Not much of a problem if you're fighting hordes, though.
Note that while this works for things like Legion Bolters and stuff, it won't work for any weapon heavier than Basic. So no dual-wielding lascannons, sorry.
A normal human could also do this with pistol-gripped (a weapon upgrade) weapons (say two autoguns) and the Two Weapon Fighter (ranged) talent. And perhaps the Ambidextrous talent, too.
Enjoy your heretical dakka, traitor!
1 Further supporting my assertion, I found this piece of text while crawling the book again (p. 244):
"If a character with the Two-Weapon Wielder (Ballistic)
Talent is armed with two pistols (or two other ranged
weapons that can reasonably be wielded in one hand)."
So one needs to be able to reasonably convince their DM that the recoil suppression on SM armor allows one-handing bolters freely. Or simply use smaller bolters.
Not sure how this applies to human characters, unfortunately.
Best Answer
No.
No one gets 1.5x Dex mod or Str mod to any weapon's attack rolls, so I will assume you are thinking damage, since a 1.5x Str bonus applies to two-handed melee weapons. However, no one gets a bonus to damage, Str or Dex, when using projectile weapons in Pathfinder.
It's on Page 141 of the Pathfinder core rulebook I have, under projectile weapons.