From what this says it was the Iroquois that named it and that makes sense.
https://www.bing.com/search?q=what+...&refig=748ed3ad29e14b6db5721fed8845ae92&pc=HC
Lake Ontario’s name comes from an Iroquoian word — oniatarí:io (also recorded as kanadario or Ontarí'io) — meaning “lake of shining waters” or “sparkling water”
. This term was used by Indigenous peoples long before European colonization, and it predates the creation of the Canadian province of Ontario by centuries
The lake’s name was adopted by early French explorers in the 17th century, appearing on maps as early as 1641 and 1656
. The Iroquoian peoples who lived in the region, including the Haudenosaunee (Iroquois) and related groups, were the original stewards of the lake’s waters and surrounding lands
. The Huron–Wendat Nation, part of the Iroquoian linguistic family, also inhabited parts of the lake’s shores in the 17th century
while the name “Lake Ontario” is now associated with the Canadian province, it was not named after the province — the province adopted the name much later, in 1867
. The original name was given by Indigenous peoples, reflecting their deep connection to the lake’s waters and their role as its long-time caretakers