I'd be more concerned about the 8 weeks than a 12 hour drive. I understand why a breeder might want to have you pick up a pup at 8 weeks, but as an owner you'll pay for that because you'll have a lot more socialization to handle.
As Zande says, 12 hours is too long for a puppy so you'd have to stop. I don't see that as a big deal because 12 hours is too long to drive without stopping. In fact I don't know any vehicle that would let you drive for that long without at least one -- more likely two -- stops for gas.
No matter the method you may get a lot of howling/crying/wimpering.
The safety record of many airlines is atrocious. IIRC United is at the bottom of the pile but some others are also not very good. Likely not an issue for you since without a direct flight air is not a reasonable alternative.
Completely OT, I've noticed that people in cities with a lot of congestion -- think LA -- give travel duration in time rather than miles. LOL