I've come across this phrase (逢へさうな) and don't really understand what's going on grammatically. It's in the context of haiku poetry, I'm assuming the kanji reading is just "a" as in "逢う", but I can't find this form elsewhere online to know if it's an idiom or a particular conjugation of the verb. Any insight would be appreciated.
This is not particle-へ.
Rather it is old kana orthography and さう sound-shifted to そう. In modern orthography it is
(Many monolingual dictionaries list old kana orthography of the entries where applicable, but of course the particular inflection あへさう would not be listed under あう.)