Canceling and Cancelling are both correct. Canceling is American English and Cancelling is British English.
There are many spelling differences between North American English and British English.
American English does not use the double L.
When to use double L in British English
You need to use a double l in British English when the word has a vowel, then an l, and then another vowel.
Other English speaking countries
Ireland, Canada, Australia, and New Zealand all follow British spelling rules although this is changing as American English dominates the world.
Spelling of Cancellation
Cancellation is always spelled with double L