Middle path in refered are based on:

• Avoiding Extreme View
• Avoiding Extreme Practices
• Avoiding Unwholesome Roots or Metal States

In each case what is chosen as the Middle is:

• Noble 8 Fold Path
• Dependent Origination
• Jhana is Also the Middle Way

Avoiding Extreme View

• Kaccā(ya)na.gotta Sutta - extreme regarding everything exists and do not exist is not right, this also leads to the notion of self and the middle teaching is dependent origination

“This world, Kaccāna, mostly depends upon a duality: upon (the notion of) existence and (the notion of) non-existence.

But for one who sees the arising of the world as it really is with right wisdom, there is no notion of non-existence regarding the world.

And for one who sees the ending of the world as it really is with right wisdom, there is no notion of existence regarding the world.

This world, Kaccāna, is mostly bound by fixation [attachment], clinging and inclination.

But this person (with right view) does not engage in, cling to, incline towards that fixation and clinging, the latent tendency of mindset and inclination—he does not take a stand (that anything is) ‘my self’.

...

‘Everything is [all exists] (sabbam atthi),’ Kaccāna, this is one extreme. ‘Everything is not [all does not exist] (sabbam n’atthi),’ this is the second extreme.

Without resorting to either of these extremes, the Tathāgata teaches the Teaching by the middle:

With ignorance as condition, there are volitional formations;

...

• Lok’āyatika Sutta - extreme regarding everything exists and do not exist is not the right view and the middle teaching is dependent origination

(1) “What now, master Gotama, do all [do everything] exist (sabbam atthi)?” “‘All exist,’ this, brahmin, is the oldest world-view [cosmology].”

(2) “What now, then, master Gotama, do all not exist (sabbam n’atthi)?” “‘All do not exist,’ this, brahmin, is the second world-view.”

(3) “What now, then, master Gotama, is all one [is everything a unity] (sabbam ekattam)?” “‘All is one,’ this, brahmin, is the third world-view.”

(4) “What now, then, master Gotama, is all many [is everything a plurality] (sabbam puthuttam)?” “‘All is many,’ this, brahmin, is the fourth world-view.

Without tending towards any of these extremes, the Tathagata teaches the Dharma by the middle:

with ignorance as condition, there are volitional formations

...

Avoiding Extreme Practices

• Dhamma,cakka Pavattana Sutta - avoid extreme practices and the middle way is the noble 8 fold path - similarly Ariya Pariyesanā Sutta and

“Bhikshus, there are these two extremes to be avoided by one who has gone forth. What are the two?

(1) The devotion to the enjoyment of sensual pleasures—it is low, vulgar, worldly, ignoble, not connected with the goal [unprofitable], and

(2) the devotion to self-mortification—it is painful, ignoble, not connected with the goal [unprofitable].

Bhikshus, without turning to either of these extremes, there is the middle way

• Maha Saccaka Sutta, (Deva) Saṅgnrava Sutta, etc. - no need to avoid pleasure which does not give arise to unwholesome states

‘I do not fear the pleasure that has nothing to do with sensual pleasures and unwholesome states!’

Avoid Unwholesome Roots

• Dhamma,dayada Sutta

Here, avuso, greed (lobha) is bad, and hate (dosa) s bad. There is the middle way for the abandonment of greed and hate, that gives rise to vision, to knowledge, to peace, to direct knowledge, to awakening, to nirvana.

And what, avuso, is this middle way? It is this very noble eightfold path,

• Maha Saccaka Sutta

Then, Aggi,vessana, I thought thus, ‘I recall that when my father the Sakya was occupied while I was sitting in the cool shade of a rose-apple tree, quite secluded from sensual pleasures, secluded from unwholesome states, I entered upon and abided in the first dhyana that is accompanied by initial application and sustained application, zest and joy born of seclusion.

Could that be the path to awakening?’

Then following on that memory, Aggi,vessana, I realized, ‘That is the path to awakening!’

I thought thus, ‘Why do I fear the pleasure that has nothing to do with sensual pleasures and unwholesome states?’

• (Deva) Saṅgnrava Sutta

Then, Bhāra,dvāja, it occurred to me, ‘I recall that [during the ploughing festival]132 when my father the Sakyan was occupied, while I was sitting in the cool shade of a rose-apple tree, quite secluded from sensual pleasures, secluded from unwholesome states, I entered upon and dwelled in the first dhyana that is accompanied by initial application and sustained application, zest and joy born of seclusion. Could that be the path to awakening?’

Then, Bhāra,dvāja, following on that memory, I realized, ‘That is the path to awakening!’

• See Dhyana by Piya Tan, section on Middle Way

In the Majjhima Nikaya, the Buddha gives his monks a discourse on the "The Exposition of Non-Conflict". In here he mentions the Middle Way:

"Here, bhikkhus, the Middle Way discovered by the Tathagata avoids both these extremes; giving vision, giving knowledge, it leads to peace, to direct knowledge, to enlightenment, to Nibbana. It is a state without suffering...and it is the right way. Therefore this is a state without conflict.

That is what the Blessed One said. The bhikkhus were satisfied and delighted in the Blessed One's words.

-- MN 139: Araṇavibhaṅga Sutta

In the Samyutta Nikaya, The Buddha also mentions the Middle Way. Here in the "The Book of the Six Sense Bases":

"There are, headman, these two extremes which should not be cultivated by one who has gone forth into homelessness: the pur­suit of sensual happiness in sensual pleasures, which is low, vul­gar, the way of worldlings, ignoble, unbeneficial; and the pursuit of self-mortification, which is painful, ignoble, unbeneficial.

Without veering towards either of these extremes, the Tathagata has awakened to the middle way, which gives rise to vision, which gives rise to knowledge, which leads to peace, to direct knowledge, to enlightenment, to Nibbana. And what is that mid­dle way awakened to by the Tathagata, which gives rise to vision . . . leads to Nibbana?

It is this Noble Eightfold Path; that is, right view . . . right concentration. This is that middle way awakened to by the Tathagata, which gives rise to vision, which gives rise to knowledge, which leads to peace, to direct knowledge, to enlightenment, to Nibbana.

-- Samyutta Nikaya: IV. The Book of the Six Sense Bases (Saḷāyatanavagga)

In the Anguttara Nikaya, The Buddha mentions the Middle Way in relation to the practice of meditation:

“Bhikkhus, there are these three ways of practice. What three? The coarse way of practice, the blistering way of practice, and the middle way of practice".

“And what is the middle way of practice? Here, a bhikkhu dwells contemplating the body in the body, ardent, clearly comprehending, mindful, having removed longing and dejection in regard to the world. He dwells contemplating feelings in feelings . . . mind in mind . . . phenomena in phenomena, ardent, clearly comprehending, mindful, having removed longing and dejection in regard to the world. This is called the middle way of practice. “These, bhikkhus, are the three ways of practice.”

-- Anguttara Nikaya 156: Ways of Practice: Establishments of Mindfulness

SN 56.11:

"There are these two extremes that are not to be indulged in by one who has gone forth. Which two? That which is devoted to sensual pleasure with reference to sensual objects: base, vulgar, common, ignoble, unprofitable; and that which is devoted to self-affliction: painful, ignoble, unprofitable. Avoiding both of these extremes, the middle way realized by the Tathagata — producing vision, producing knowledge — leads to calm, to direct knowledge, to self-awakening, to Unbinding.