Had French trappers already explored the areas explored by Lewis & Clark?

Answer 1

Specific exploration, no. Trappers had traveled through some of the areas, in pursuit of whatever they were trapping.

Answer 2

Yes. People had already been where they went period. Spanish and Sir Francis Drake had already explored the Southern Pacific coast. Russians the Northern northwest coast. French trappers got everywhere just about. Lewis and Clark led a scientific expedition to find out just what America had bought from France in the Louisiana Purchase. They were not the first Europeans there. Even legends of shipwrecked junks existed in the northwest and for sure several Manila Galleons were blown off course and wrecked in the northwest.

Answer 3

Some of it.
One of the purposes of the expedition was to scout out British and French activity in the area for trade opportunities or possible political/economic competition. The entire western half of the Mississippi watershed was legally French until Jefferson bought it, and there had probably been French trappers in the area since New Orleans was founded in 1718.
However, in Oregon there has been no record of French activity. The Americans, British, Spanish, and Russians all had claims to the area, but not the French. Even the British only ever had a single expedition reach Oregon overland (Alexander MacKenzie). All four claimants also had some activity off the Oregon coast, but for the French, who now only had claims to areas in and around the Caribbean, this was just too far out of the way.

Answer 4

No- they had gone into the Plains and as far as the upper Missouri, but Lewis and Clark went OVER the mountains to the Pacific- far farther than anyone had ever done before.