Past Buddha's : Sources I came  along with this (http://www.aathaapi.net/dwncounter.php?number=29)  detailed description of the Buddhas (during vag and mano pradani era of Gautama Bodhisattva) before the 28 Buddhas. 512000 in number to be exact. I have also heard about this fact in some texts as well. 

Is this stated in the pali canon? What are the sutras?
I would check out the (dubious) Digha Nikaya, particularly the Mahāpadāna Sutta.


  It is now ninety-one aeons ago, brethren, since Vipassī, the Exalted One, Arahant, Buddha Supreme, arose in the world. It is now thirty-one
  aeons ago, brethren, since Sikhi, the Exalted One, Arahant, Buddha
  Supreme, arose in the world. It was in that same thirty-first aeon,
  brethren, that Vessabhu, the Exalted One, Arahant, Buddha Supreme,
  arose in the world. It was in this present auspicious aeon, brethren,
  that Kakusandha, the Exalted One, Arahant, Buddha Supreme, arose in
  the world. It was in this auspicious aeon, brethren, that Koṇāgamana,
  the Exalted One, Arahant, Buddha Supreme, arose in the world. It was
  in this auspicious aeon, brethren, that Kassapa, the Exalted One,
  Arahant, Buddha Supreme, arose in the world. It is in this auspicious
  aeon, brethren, that now I, an Arahant, Buddha Supreme, have arisen in
  the world.


MN 50 also contains a story.


  Venerable Mahāmoggallāna saw the Evil One stuck in the throat and said, I see you there too. You are stuck in the throat. In the past
  there was an Evil One named Dūsi. To me there was a sister named Kāli.
  You were her son. Then you were my nephew. It was at the time of the
  perfect rightfully enlightened Blessed One Kakusanda's time. To the
  perfect rightfully Enlightened One, Kakusanada, there were two chief
  disciples named Vidura and Sañjīva


(Disclaimer: Based on human &amp; social evolution, I personally doubt there were any past Buddhas. For example, the Mahāpadāna Sutta appears state the very first Buddha had 6,800,000 or 68 lacs arahant disciples; the older the Buddha, the more arahant disciples they had, which seems to contradict historical evidence of human population. The above genre of suttas that number a handful among 1,000s of suttas, which also contradict SN 22.79 in talking about literal 'personal' past lives, I would speculate were later writings rather than words of the Buddha.)