Mix sliced cucumbers and onions and sprinkle with the coarse salt. Cover with ice cubes and let stand for 3 hours.
To make brine, combine sugar, vinegar and spices in a large kettle. Bring to a boil. Drain the cucumbers and onions and add them to the brine. Bring back to a boil.
Pack in hot canning jars. Process pints in a hot water bath for 5 minutes, and quarts, for 10 minutes.
NOTE: You may also pack cold cucumbers and onions in hot jars, ladle brine over them and cover with the lid and ring. Then, proceed with the hot water bath. The pickles tend to stay crisper using this method.