Here's a great resource for ID'ing suckers and any other fish present in WI.
U can keep shortheads. Several ways of telling them apart, river rh exist in large river systems in wi and depending on how fragmented the river your fishing is, rivers are likely nonexistent in your system. Another way is size, river rh are HUGE compared to shortheads. Another way is to count scales around the caudal peduncal, without looking it up pretty sure river rh have many more scales around theirs. Basically, depending on the system your fishing, your catching 99.99% shortheads just because river rh don't exist in huge numbers like shortheads, goldens, silvers