Interesting topic.
Sugar beets are big in western U. S. and western Canada. In our groceries here in Alberta, all of the sugar in larger bags, 2 kg (= short 5 lb approx.) or larger is from sugar beets.
Corn sugars as corn syrup shows up in table-size bottles but is available to manufacturers from wholesalers in large containers.
Cane sugar is kept out of the normal grocery; only found as a specialty sugar- Demerara and some of the brown, confectioners, etc. Wholesalers sell bags to those bakers and candy-makers who use it.

According to the USDA, corn as a feed grain accounts "for more than 90% of total value and production of feed grains." Some 80 million acres.
Corn syrup is a mainstay with Illinois agribusiness. Corn production for sugar seems to be subsidized. There are also very good insurance policies for producers (who determines percent of loss in the crop?).

It is hard to find information on large agribusiness corn producers; farms constituting the whole often retain names from their days of independence although control is centralized.
Dick Greenhaus, can you suggest a good publication on agribusiness and its share of the market? I would like to learn more about this. There are lots of bloggy materials, but there must be reliable figures somewhere.

Costs of production decrease as farm size increases, of course favoring the larger producer. The new genetically fiddled corns mean higher production per acre.