A word that entered English through French
The pronunciation fight makes more sense once you know where the word has been. It is not English in origin and it is not Spanish: pecan came into American English around 1712 from the French pacane, which French colonists in the Mississippi valley had themselves borrowed from an Algonquian language — most likely Illinois pakani. Related forms survive across the family: Cree pakan, Ojibwe bagaan, Abenaki pagann.
The original meaning is beautifully practical. The Algonquian term covered hard-shelled nuts generally — the ones that need a stone to crack. Long before anyone argued about the stress, the word described the work required to eat the thing.
Three pronunciations, not two
Any honest version of this match has to acknowledge a third camp, because the country genuinely splits three ways: puh-KAHN, closest to the French source and common across much of the South; PEE-can, with the stress moved forward, widespread in the North and parts of the Midwest; and pee-KAHN, a hybrid that keeps the long first vowel and the back stress, and which quietly wins in a lot of places where people insist they say one of the other two.
The joke that circulates in the South — that a PEE-can is something you keep under the bed — tells you which camp coined it, and also tells you that the stress pattern is heard as a marker of outsider status, not just as a variant.
Why the French version drifted
Stress in English tends to migrate toward the front of a word over time, especially in words borrowed from French, and especially once a word becomes common in everyday speech rather than staying technical. The same drift produced GAR-age alongside ga-RAHZH and BAL-let alongside older stress patterns.
So the two main forms are not right and wrong. They are early and late: one preserves the shape of the word as it arrived, the other shows what two centuries of American mouths did to it. Both processes are entirely normal, and both are still running.
What the dictionaries do
They list all of them. Major American dictionaries record multiple pronunciations without preference, which is the standard lexicographic response to a variant that is regionally distributed rather than socially marked — meaning nobody is judged less educated for either one, unlike the pronunciations that dictionaries do quietly flag.
Which leaves the question open in the only way that matters here. There is no authority to appeal to, no court case, no inventor to overrule the public. There is just the country, split three ways, each region convinced it is the normal one. Say it out loud before you vote — people are often wrong about which camp they are in.
Sources: etymology of "pecan" from French pacane and Illinois/Miami pakani, per standard etymological dictionaries; cognate forms in Cree, Ojibwe and Abenaki; multiple pronunciations listed without preference in major American dictionaries.