Is carrying a blaster rifle considered a dual weapon or one? So therefore...would it be the Two-Weapon Fighting feat or the Dueling feat that would help?

Sadly neither effect blaster rifles, but the ydont get penalties from using both hands.

Neither TWF nor Dueling work with ranged weapons.

 

Two-handed blasters benefit directly from points put into the Weapon Proficiency: Blaster Rifle, Weapon Focus: Blaster Rifle, and Weapon Specialization: Blaster Rifle feats.