You are correct about Valentia being essentially lowland Scotland (more closely defined as Britain north of the wall), but see below. As for Ezitannia note the following:

[of 31 presidents] ... in the Britains three: of Britannia prima; of Ezitannia secunda; of Flavia Caesariensis.
followed by :
Under the control of the worshipful vicar of the Britains:
Consulars: of Maxima Caesariensis, of Valentia.
Presidents: of Britannia prima, of Britannia secunda, of Flavia Caesariensis.

It looks to me as though “Ezitannia” is an error for “Britannia”. Look at it just right and “Ez” could easily be “Br”. If the document was scanned and put through OCR, then I suspect someone missed this one when checking over the quality of the scan. If it was transcribed by hand, then either the transcriber misread the document or the person who wrote the original had lousy handwriting (or perhaps couldn’t read the original he was copying).

Britannia Prima and Secunda and Flavia and Maxima Caesariensis were the four provinces that Diocletian divided Britain into when he reorganized the empire. There is some question about Valentia, it may have been a subdivision of Britannia Secunda or a later addition. One source I saw said it was the Midlands, but it also disagrees with everythig else I found in other particulars, so I consider that suspect. The provinces seem to correspond as follows:

Britannia Prima: Wales and the West Country with its capital at Cirencester
Britannia Secunda: the north or northeast with its capital at York
Flavia Caesariensis: the northwest or center with its capital at Lincoln
Maxima Caesariensis: the southeast with its capital at London