Who explored the Atlantic coastline of North America for France while looking for the Northwest Passage?
The name of the person you are asking about is Jacques Cartier. Cartier was a French explorer who sailed the Atlantic coast of North America looking for the Northwest Passage.
Even after the New World was “discovered,” European explorers still thought they could get through to Asia without going around the southern tip of South America. This would have been a very good thing as it would have saved them a great deal of time on each voyage from Europe to Asia. We know today that there is no Northwest Passage, but we see the value of such a thing from the value of the Panama Canal, which also allows ships to go from the Atlantic to the Pacific without rounding South America.
Jacques Cartier was a Frenchman born in 1491. He made three voyages of exploration for France in the 1530s and 1540s. His main goal was to find a Northwest Passage. What he ended up finding was the St. Lawrence River. He navigated up the river until he reached impassable rapids at what is now Montreal.
The French explorer who looked for the Northwest Passage, then, is Jacques Cartier.