Whisk the cane sugar and juice together over medium heat until the cane sugar is dissolved. Do not let the mixture boil. Let it cook for 5-10 minutes, stirring occasionally.
Spread an old kitchen towel on the counter. Use your jar lifter to remove heated jars from the canner, drain, and line them up on the towel. Use a funnel and ladle and add the crabapple syrup to warm jars, making sure to leave ¼-inch headspace. Wipe the rims with a clean cloth. Use your magnetic lid lifter to lift lids out of the warm water, center the lid on the jar, and screw on the band until it is fingertip tight. Do not overtighten.
Using the jar lifter, place jars carefully into the canner leaving space between them. You do not want them to be touching. When the jars are all in the canner, add more boiling water so the water level is at least one inch above the jar tops. I boil water in my kettle and have it ready to go for this reason. Pour the water around the jars and not directly onto them.
Cover the canner with the lid and bring the water to a boil over high heat. Once the water boils, continue boiling for 10 minutes. When the processing time is complete, turn off the heat.
Place an old kitchen towel on your counter to place your hot jars on. They cannot be moved for about 24 hours, so make sure it is in a spot where they won't be disturbed. Remove the lid of the canner by tilting the lid away from you so that steam does not burn you. Use a jar lifter to lift jars carefully from the canner and place the jars on the towel.
Allow the jars to cool for 12 to 24-hours. When you hear the "ping" or "pop" you know that your jars are sealing. I usually do a little happy dance at this point.
Let the water in the canner cool completely before emptying it.
After about 12 to 24 hours, check the jars to see if the lids have sealed by pushing on the center of the lid. The lid should not pop back. If the lid bends up and down, it did not seal. Place that jar in the fridge and use it up first.
Wipe the outside of the jars with a clean cloth to remove any sticky residue. Label and date your jars. Store your lovely homemade crabapple syrup in a cool, dark place and use it within 12 months.
If you want to store the syrup in the fridge, just let the syrup cool completely and pour the cooled syrup into bottles or sterilized canning jars and then store it in the fridge. The syrup will keep in the fridge for several months.