Slice cucumbers in 1/4 inch slices. Slice onions thinly and place cucumbers, salt and onions in a large bowl or pan and mix carefully.
Place a clean towel on top of the cucumber mixture, cover with ice and place in the refrigerator to chill for 4 hours
When cucumber mixture is almost done chilling, prepare the canner by filling 3/4 full with water and set on the stove on high. This will take some time to get to boiling. In the mean time, be sure your jars are washed.
Place rings and lids in a small pot of water and bring to a boil. Turn off the heat and let sit in the hot water until you are ready to use them.
After the 4 hours is up, put the cucumber mixture into a colander and rinse well. Let drain and then rinse again. Let drain.
When the canner pot is boiling, fill the clean jars with some of the hot water from the canner and let sit in the canner for 5 minutes.
While the jars are sterilizing, you can prepare the pickle brine. Add the vinegar, sugar and all spices to a 6-8 quart pot and place on the stove on high. Once it begins boiling, add the pickle and onion mixture. Stir. Bring back to a boil and then turn off the heat.
Take out your canning jars using the jar lifter and dump the hot water back into the canner pot.
Using a slotted spoon, fill the hot jars with pickle/onion mixture. Fill to 1 inch from the top of the jars. Then fill the jars to 1/2 inch from the top with the brine/syrup.
After the jars are filled, use a butter knife to slide down the sides of the jars in an up and down motion to help get the air pockets out.
Wipe the tops of the jars with a clean, damp cloth or paper towel and place the lids and tighten the rings.
Using the jar lifter, place the jars in the water bath canner making sure the water is 1 inch above the tops of the jars. Add more HOT water if needed and replace the lid. Bring the canner to a boil and let boil for 15 min. (may need to boil longer depending on your elevation)
Remove the pickle jars from the canner and set on a towel on the counter, making sure there is space between them. Let cool. You should hear popping sounds within 10min. or so letting you know the lids are sealing. Once the jars are cool, check each lid by pressing down on the tops. If they pop back up then they are not sealed and you'll need to put the jar in the refrigerator.