Sorry, No help on pool 3.
Pool 4. As suggested, Frontenac Beach offers some walleye fishing. Hok-Si-La beach nearer to Lake City may offer some walleye fishing but historically its been either a very, very early day or late afternoon/early evening bite there.
Baypoint Harbor and Lake City’s sailboat harbor areas can offer some panfishing. If you have patience Trailer Point on the up-stream side in Lake City can hold crappies but you really have to search them out. Wabasha Harbor sees a lot of panfish traffic and the backwaters of pool 4 start right across the high bridge from Wabasha. Wilcox Landing is pool 4″ last backwater hurrah and is located just south and to the left of the high school on old 61. Below Kellogg you’ll find extensive backwaters as well in pool 5.
IF you hit the backwaters off the dike road between Wabasha and Nelson, Wisconsin just be aware that there is an area of substantial current on the upstream side of the road, or to your left as you travel from MN to WI. Ice there can be a problem so I suggest fishing those areas to your right as you travel the same. You’ll find a million community spots along that road but if you slip away from the crowds you can often hit on real good fishing and much better fish.
Do yourself a favor and look up the MN DNR’s website and search for publications. Look for “Mississippi River Guide”, the one specific to the area between Hastings, MN and the Iowa border. Ask them to send you a copy. Its a free book and darned near 100% is maps which show the channel and backwaters along with towns and landings by name. This is super handy to have at home just to study and look for possible new water to fish but its also a handy visual reference to get to the places I have mentioned.