Limited experience on the Niagara but I'll tell you what I have seen. 1st off, never have seen either oldsquaw or scoters on the river, have heard of oldsquaw being shot but never scoter. Outside of bufflehead I've only seen a handful of divers before the 2nd season.
2nd season I've seen a whole lot of divers, g-eye, cans, redheads, bluebills, ringnecks, b-head.
Pardon the ignorance on my part but do you differentiate between "divers" and "sea ducks"???