First, let's simplify each set of parentheses:

3a² - a + 2
-3a² + 3a - 1
a² - 1

Now, let's add or subtract each term:

(3a² - a + 2) + (-3a² + 3a - 1) - (a² - 1)
= 3a² - a + 2 - 3a² + 3a - 1 - a² + 1
= (3a² - 3a² - a + 3a - a²) + (2 - 1 + 1)
= (-a + 3a - a) + 2
= 2a + 2

Therefore, the simplified expression is 2a + 2.