believe it or not, bodhisatta vows this incident is indeed mention in the pali canon.
I don't believe so. In fact, there is one sutta which strongly suggests that Gotama never undertook any form of bodhisatta vow.
http://www.accesstoinsight.org/tipitaka/an/an10/an10.095.than.html
"And, Master Gotama, when having directly known it, you teach the Dhamma to your disciples for the purification of beings, for the overcoming of sorrow & lamentation, for the disappearance of pain & distress, for the attainment of the right method, & for the realization of Unbinding,
will all the cosmos be led [to release], or a half of it, or a third?"
When this was said,
the Blessed One was silent.
Then the thought occurred to Ven. Ananda: "Don't let Uttiya the wanderer acquire the evil viewpoint that, 'When I asked him an all-encompassing question, Gotama the contemplative faltered and didn't reply. Perhaps he was unable to.' That would be for his long-term harm & suffering." So he said to Uttiya, "In that case, my friend, I will give you an analogy, for there are cases where it is through the use of analogy that intelligent people can understand the meaning of what is being said.
"Uttiya, suppose that there were a royal frontier fortress with strong ramparts, strong walls & arches, and a single gate. In it would be a wise, competent, & knowledgeable gatekeeper to keep out those he didn't know and to let in those he did. Patrolling the path around the city, he wouldn't see a crack or an opening in the walls big enough for even a cat to slip through. Although he wouldn't know that 'So-and-so many creatures enter or leave the city,' he would know this: 'Whatever large creatures enter or leave the city all enter or leave it through this gate.'
"
In the same way, the Tathagata isn't concerned with whether all the cosmos or half of it or a third of it will be led to release by means of that [Dhamma]. But he does know this: 'All those who have been led, are being led, or will be led [to release] from the cosmos have done so, are doing so, or will do so after having abandoned the five hindrances — those defilements of awareness that weaken discernment — having well-established[1] their minds in the four frames of reference, and having developed, as they have come to be, the seven factors for Awakening. When you asked the Blessed One this question, you had already asked it in another way.[2] That's why he didn't respond."