Up in Minnesota and Wisconsin they're mostly dependent on rain through the summer months. Here is a site with the popular runs and the gauges: Rapids Riders
Minnesota has some fun water but most of the steep creeks run for 1 week in March/April but will go (for like a day or two) if they get enough rain. The Saint Louis river, which is south of Duluth, MN maintains a constant flow with something like 6 releases and has high quality (though short) rapids.
If you're familiar with WI then you know about the Wausau park and it's releases: Welcome to the Wausau canoe / kayak corporation website
The rapids riders forum discusses the various releases out of this dam or that (like jim falls).
The U.P. is the same as the MN steep creeks that drain into Superior, but again, rain dependent outside of the winter melt.
Are you traveling there?