Population growth

With the assumption that civilization continued for million of generations / while the sun provided a suitable environment,

what would the average population growth per year or per generation be?

Zero.

Going to extremes with the assumption that in a billion years (40 million current generations) the entire mass of the planet consists only of intelligent beings weighing 1 kg each (i.e., on the order of 6 times 10 to the 24 individuals), the average annual rate of growth from a starting base of 7 billion would be less than 0.000001%, (about 3 millionths of a percent or about 200 per year more born than dying at the current level). Assuming there would only be 1 individual left, the average annual rate of population reduction would likewise be less than 0.000001%.

Fluctuations in between, either way, need to cancel each other out in the long run. On comparison, with an average growth of 1%, it would need less than 3,500 years (the pyramids are much older) to reach the mass of the earth with individuals weighing only 1 kg from the current level (with heavier individuals). At baby boomer 2%, it would take less than 1800 years.

Continued exponential growth over long periods is impossible. Life will become very tough by external factors containing growth unless we find ways to contain it, and humanity will quickly be extinct unless there are mechanism to keep if from falling too low.