If you have a boat,the St.Marys off-channel marsh complexes offer pretty consistent hunting, particularly now that the water levels have increased roughly 18", putting "fresh" production back into action... Basically, these marshes exist in good quantity down to Lime Island.
The St. Marys River is essentially a series of shalllow interconnected lakes, knitted together via connecting channels that have been dredged for ship passage. These freighters displace a large amount of water into the off-channel areas on passage, so be careful to not get caught in the shallow during one of these events-easily a 20" water level change on average, with waves up to 3-4" in shoal water areas, particularly if their pilot is pusing the throttle a bit(pretty common in the downbound sections).
Divers work the river channel for the most part, settling in several large shoal water areas in Lake Nicolet, Lake George,Munuscong Bay, Duck Bay, and Potaganissing Bay. Puddlers can be anything from teal to wigeon. Mallards and decent black duck numbers are the norm, but I have taken pintail, wood ducks, wigeon and some gadwalls over the years.
Google Earth is an excellent remote scouting tool, particularly for duck hunters looking for beaver floodings, with one caveat: Note the date of the aerial photo, since it is not current, water levels may have changed. As you move the cursor, you will have updated GPS coordinates readily available to go out and ground truth what you are interested in scouting and to obtain permission on private holdings.
Dafter area farms hold excellent numbers of migration Southern James Bay population Canadas. There is also a pretty good resident Canada flock in pockets along the river. The soils in the eastern UP are old sea bed remants, so they clay-laden and hold water well. This year's consistent rains will offer a lot of sheetwater that will spread birds out inland.
Cedarville/Hessel area marsh complexes can off some excellent waterfowl hunting as well, particularly after the opener.