Annual Crops Requiring Only Field Drying

Two years ago we bought an 18 acre farm 12 km east of Fergus, Ontario, that has about 12 acres workable. The land had been left alone for 15 years. Last year we had a local farmer plant oats and barley. This year we would like to plant some form of herb. Our soil is sandy loam, and is well drained after June. Prior to that there is a 2 acre area that is wet.
We would like to have the herb sown and harvested in the same year, and we will use local contractors to do this work.
Are there herbs that don't need to be dried, other than field/air drying? Also direct seed sowing, rather than plugs.

Very few. None which would produce quality product that would fetch a decent price. We suppose you might consider alfalfa and oatstraw, but these are not in great demand.
There are some seed crops that could be grown, but even these require some drying and processing. These include evening primrose, coriander, caraway, borage, and others. Coriander, caraway and borage are significant crops on the prairies and farmers typically grow tens or hundreds of acres. These may not be economic on the small acreage you are contemplating.

Is it possible to pre-sell one's crop?

Rarely. Most buyers require samples even before they talk to a new grower.

What poundage will each acre produce?
What herb produces the highest net or gross profit?

The largest profits per acre are made on crops that require significant inputs, especially labour. Most of these require plugs and many are perennial crops. Crops that require few inputs are typically low revenue producers on a per acre basis.
Richard Alan Miller's book "The Potential of Herbs as a Cash Crop" is recommended as an introduction to herb farming. It gives an excellent overview of the business, including prices, yields, equipment requirements, and market potential on a variety of crops. The book is available from Richters.