In American English, the verb cancel is usually inflected canceled and canceling—with one l. This is not a rule, however, and exceptions are easily found. In varieties of English from outside the U.S., including Canadian, British, and Australian English, cancelled and cancelling are the preferred spellings.
The spelling distinction extends to cancelers and cancellers, as well as to cancelable and cancellable, but it does not not extend to cancellation, which everywhere is spelled with two l’s.
As the Ngram below shows, American English has only recently adopted the one-l spellings of canceled, canceling, etc., and the change is not fully engrained in the American language. In web searches of American publications covering the last couple of years, cancelled and cancelling still appear about once for every five instances of canceled and canceling. Outside the U.S., meanwhile, the one-l spellings appear only very rarely. This is true even in Canada, which is usually friendlier to American spelling idiosyncrasies than is the rest of the English-speaking world.
This Ngram graphs the use of canceled and cancelled (as a percentage of all words used) in American books, journals, and magazines published from 1800 to 2000:
Similar Ngrams for British books show the one-l forms beginning to gain ground in British English—likely due to the strong American influence on web-only publications from around the world—but the two-l forms still prevail by a large margin.
Here are a few examples from American news sources:
Exeter High School principal Vic Sokul has canceled dances for the rest of the school year. [New Hampshire Exeter]
Canceling the contract would be cheaper but not cheap. [Chicago Tribune]
Many flights have been canceled, forcing more passengers to connect at big and increasingly crowded hubs. [New York Times]
Under current law, it is scheduled to rise to 6.8% on July 1, an increase that Obama has called for canceling. [Los Angeles Times]
Moriarty added that an earlier cancellation could have allowed the slot to be resold, which would have resulted in a credit being issued. [Boston Globe]
Cancelled and cancelling, as used in the following examples, are preferred everywhere else::
Allegations of black market touting by foreign Olympic committees could see thousands of tickets cancelled. [Independent]
Student groups say organizers of the Canadian Grand Prix overreacted in cancelling the free opening day of the event. [CBC]
A New Zealand freediving champion plunged to 125m on a single breath only to have what would have been a world record cancelled. [New Zealand Herald]
It emerged yesterday that the girl, named only as Merthe, had gone into hiding with her family after cancelling the party. [Irish Times]