In a glass or stainless steel bowl, combine cucumbers, onions, and salt.
Mix well, cover with cold water, and let stand at room temperature for 2 hours.
Transfer to a colander placed over a sink, rinse with cool running water, and drain thoroughly.
Meanwhile, prepare canner, jars, and lids.
In a large stainless steel saucepan, combine vinegar, sugar, mustard seeds, celery seeds, and turmeric. Bring to a boil over medium-high heat, stirring to dissolve sugar. Stir in vegetables and return to a boil.
Pack vegetable into hot jars to within a generous ½ inch of top of jar. Ladle hot pickling liquid into jar to cover vegetables, leaving ½ inch headspace.
Remove air bubbles and adjust headspace, if necessary, by adding hot pickling liquid. Wipe rim. Center lid on jar. Screw band down until resistance is met, then increase to fingertip tight.
Place jars in canner, ensuring they are completely covered with water. Bring to a boil and process for 10 minutes. Remove canner lid.
Wait 5 minutes then remove jars, cool, and store.