The name of the town did not change. Nor did the correct spelling change. But the language the officials spoke did.
Sânmihaui is not a German word and, while Romania (like the rest of the Austro-Hungarian empire) had a fair number of German speakers), its official language (and/or the language when the town was named) was different. Depending on the year and exact location: Romanian, Hungarian, Ukrainian, etc.
It appears that, by 1923, the date of your document, Romanian was the official language of Romania. But past town names could have been in other languages and also other scripts.
Sanmihailul is very similar to Sânmihaui aside from the ending. The document is Canadian and "â" is not a letter in English. I'll note that the town is listed as "Samnihailiel" elsewhere in the document and appears to be a less careful rendition, though still basically the same thing.
Sânmihaiu Român (Hungarian: Bégaszentmihály) is a commune in Timiș
County, Romania. It is composed of three villages: Sânmihaiu German
(Németszentmihály; German: Deutschsanktmichael), Sânmihaiu Român and
Utvin (Ötvény). (ref)
It's interesting that the actual village was probably "Sânmihaiu German" and the German name for that was "Deutschsanktmichael" (In English we'd say "German Saint Michael.) The end of that sounds like "lul," the ending given in the Canadian document. Perhaps a coincidence, perhaps a local nickname?
As for who filled it out...it was not the 2 year old named in the document. And it was not the family member (father I assume) who signed it (handwriting is different). The handwriting matches the signature of the booking agent in Antwerp, Belgium...a notation also says Bucharest, which is in Romania, which may indicate where they bought their ticket, but it's unlikely the agent traveled with them since Bucharest is not on the ocean.