What is the most agreed idea of Sunni scholars about watching Allah in the Hereafter?
It is confirmed by the Quran, Sunnah, and consensus of the Pious Salaf that the believers will see Allah with their eyes on the day of the Judgement.
Do all Sunni scholars have the same idea about this?
Yes.
What is the reasoning behind their ideas?
Evidence for any belief about Allah is from Qur'an and Sunnah. While, in this post the verses which are evidence for this belief is quoted, it is also proven by overwhelming number of Sahih Hadiths. I quote some of them here (emphasis mine):
Suhaib reported the Apostle (may peace be upon him) saying: When
those deserving of Paradise would enter Paradise, the Blessed and the
Exalted would ask: Do you wish Me to give you anything more? They
would say: Hast Thou not brightened our faces? Hast Thou not made us
enter Paradise and saved us from Fire? He (the narrator) said: He
(God) would lift the veil, and of things given to them nothing would
he dearer to them than the sight of their Lord, the Mighty and the
Glorious.
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عُمَرَ بْنِ مَيْسَرَةَ، قَالَ
حَدَّثَنِي عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، حَدَّثَنَا حَمَّادُ بْنُ
سَلَمَةَ، عَنْ ثَابِتٍ الْبُنَانِيِّ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ
أَبِي لَيْلَى، عَنْ صُهَيْبٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ
" إِذَا دَخَلَ أَهْلُ الْجَنَّةِ الْجَنَّةَ - قَالَ - يَقُولُ
اللَّهُ تَبَارَكَ وَتَعَالَى تُرِيدُونَ شَيْئًا أَزِيدُكُمْ
فَيَقُولُونَ أَلَمْ تُبَيِّضْ وُجُوهَنَا أَلَمْ تُدْخِلْنَا الْجَنَّةَ
وَتُنَجِّنَا مِنَ النَّارِ - قَالَ - فَيَكْشِفُ الْحِجَابَ فَمَا
أُعْطُوا شَيْئًا أَحَبَّ إِلَيْهِمْ مِنَ النَّظَرِ إِلَى رَبِّهِمْ
عَزَّ وَجَلَّ " . [Sahih Muslim]
and
Narrated Qais:
Jarir said, "We were with the Prophet and he looked at the
moon--full-moon--and said, 'Certainly you will see your Lord as you
see this moon and you will have no trouble in seeing Him. So if you
can avoid missing (through sleep or business, etc.) a prayer before
the sunrise (Fajr) and a prayer before sunset (Asr), you must do so.'
He then recited Allah's Statement: And celebrate the praises Of your
Lord before the rising of the sun and before (its) setting." (50.39)
Isma`il said, "Offer those prayers and do not miss them."
حَدَّثَنَا الْحُمَيْدِيُّ، قَالَ حَدَّثَنَا مَرْوَانُ بْنُ
مُعَاوِيَةَ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، عَنْ قَيْسٍ، عَنْ جَرِيرٍ،
قَالَ كُنَّا عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَنَظَرَ إِلَى
الْقَمَرِ لَيْلَةً ـ يَعْنِي الْبَدْرَ ـ فَقَالَ " إِنَّكُمْ
سَتَرَوْنَ رَبَّكُمْ كَمَا تَرَوْنَ هَذَا الْقَمَرَ لاَ تُضَامُّونَ
فِي رُؤْيَتِهِ، فَإِنِ اسْتَطَعْتُمْ أَنْ لاَ تُغْلَبُوا عَلَى صَلاَةٍ
قَبْلَ طُلُوعِ الشَّمْسِ وَقَبْلَ غُرُوبِهَا فَافْعَلُوا ". ثُمَّ
قَرَأَ {وَسَبِّحْ بِحَمْدِ رَبِّكَ قَبْلَ طُلُوعِ الشَّمْسِ وَقَبْلَ
الْغُرُوبِ}. قَالَ إِسْمَاعِيلُ افْعَلُوا لاَ تَفُوتَنَّكُمْ.
[Sahih Bukhari]
There are many hadiths regarding the same event.
If some (or all) believe we are able to see Allah in the Hereafter, do they mean seeing him the same way we see any other object now?
Your doubt regarding how we will see Him (Subhanahu wa ta'ala) is cleared by the statement of the Prophet(salallahu alayhi wassalam) in several hadith:
Abu Hurairah narrated that the Messenger of Allah (s.a.w) said: "Do
you crowd one another in order to see the moon on the night of a full
moon? Do you crowd one another in order to see the sun?" They said:
"No." He said: "So verily, you shall see your Lord as you see the moon
on the night of a full moon, you shall not crowd one another to see
Him." (Sahih)
That we will see Him with our own eyes:
Narrated Jarir bin `Abdullah:
The Prophet said, "You will definitely see your Lord with your own
eyes." [Sahih Bukhari]
And you will have no trouble seeing Him:
Abu Hurairah said : The people asked : Messenger of Allah! Shall we
see our lord, the Exalted, on the Day of resurrection? He replied : Do
you feel any trouble in seeing the sun at noon when it is not in the
cloud? They said: No. He asked : Do you feel any trouble in seeing the
moon on the night when it is full and not in the cloud? They replied:
No. He said: By him in whose hand my soul is, you will not feel any
trouble in seeing him except as much as you feel in seeing any of
them. [Sunan Abi Dawood]
You can read several other Ahadeeth and statements of the Salaf and Scholars of the Ummah regarding the belief here. It is a compendium of all the evidences.
