I did this river years ago when I was a beginning canoeist. I cannot
imagine the rapids becoming class III-IV under any circumstances -
there's just not enough gradient. I do remember that there's a
damkeeper upstream. We did the run at a very minimal level, and he
told us afterwords that had he known we were going to paddle, he would
have released more water for us.

Sorry, don't remember enough to comment about shuttles. We had a group
and did our own. I do remember that the riverside camping was quite
nice. First night we slept on Canadian soil (river left) and second on
American (river right.)