Well, in Bellini's own times, all the tenors were singing in falsettone the high notes. The first Pollione himself, Domenico Donzelli, was using this technique for anything above a G3.
Bellini wanted for the role not Donzelli, but Rubini, only he was not available for the premiere (later, Rubini sang the role at Théâtre des italiens, with Bellini already dead), and he adapted a bit the role to Donzelli's voice.
The voice of Donzelli was rather limited as a coloratura performer. He was the owner of baritonal-like voice, that was singing in full voice up to the high G, and then, using 'falsettone' was able to sing up to a high C (in "Meco all'altar di Venere", Bellini tried to use the capabilities of Donzelli, but he marked the high C as optional, nevertheless).
Of course, we can't know for certain what falsettone was, as of course there are not any recordings from the early 19th century. It was used not in all the tessitura, but only for the high notes. And the note from which it was used was different for each singer. For Rubini himself it was most probably the high C itself, or high B flat.
Also, falsettone was surely a mixed emission, including resonances from the head voice, but also some from the chest voice. In Italian, it has been described as 'pieno con consonanza di testa'. Personally, I don't think it was something fundamentally different (humans being humans in the 19th century, too) to what we can hear sometimes in the recordings of Gigli, or David Devriès.
The feared C4 in Pollione's cavatina, in the repetition of 'sensi':
Meco all'altar di Venere
era Adalgisa in Roma,
cinta di bende candide,
sparsa di fior la chioma;
udia d'Imene i cantici,
vedea fumar gl'incensi,
eran rapiti i sensi
di voluttade e amor
Has been handled in different ways: just singing the C4, not singing the C4, produce the C4 in 'voluttade', because it' easier than giving the high note on the 'i',... All of them were approved by Bellini himself before his death.
I do prefer to go for the C4, but it's not something essential. It's more important to be able to read into the score and the character. Carlo Bergonzi never sang the C4, but was a great Pollione.
Bellini wanted for the role not Donzelli, but Rubini, only he was not available for the premiere (later, Rubini sang the role at Théâtre des italiens, with Bellini already dead), and he adapted a bit the role to Donzelli's voice.
The voice of Donzelli was rather limited as a coloratura performer. He was the owner of baritonal-like voice, that was singing in full voice up to the high G, and then, using 'falsettone' was able to sing up to a high C (in "Meco all'altar di Venere", Bellini tried to use the capabilities of Donzelli, but he marked the high C as optional, nevertheless).
Of course, we can't know for certain what falsettone was, as of course there are not any recordings from the early 19th century. It was used not in all the tessitura, but only for the high notes. And the note from which it was used was different for each singer. For Rubini himself it was most probably the high C itself, or high B flat.
Also, falsettone was surely a mixed emission, including resonances from the head voice, but also some from the chest voice. In Italian, it has been described as 'pieno con consonanza di testa'. Personally, I don't think it was something fundamentally different (humans being humans in the 19th century, too) to what we can hear sometimes in the recordings of Gigli, or David Devriès.
The feared C4 in Pollione's cavatina, in the repetition of 'sensi':
Meco all'altar di Venere
era Adalgisa in Roma,
cinta di bende candide,
sparsa di fior la chioma;
udia d'Imene i cantici,
vedea fumar gl'incensi,
eran rapiti i sensi
di voluttade e amor
Has been handled in different ways: just singing the C4, not singing the C4, produce the C4 in 'voluttade', because it' easier than giving the high note on the 'i',... All of them were approved by Bellini himself before his death.
I do prefer to go for the C4, but it's not something essential. It's more important to be able to read into the score and the character. Carlo Bergonzi never sang the C4, but was a great Pollione.