I am confused about the spelling of the past tense of the verb "cancel". I googled a bit but everyone has a different opinion apparently. I need to know the correct standard spelling.
As @StoneyB points out, both are correct.
Having been taught that a single consonant at the end of a word would make
canceled be pronounced as "can-sealed" and a double consonant would make
cancelled be pronounced as "can-selled", I use cancelled even though the present tense is spelled cancel.
Google Ngrams shows (for what it's worth):
Clearly canceled has over taken cancelled, but that may be an artifact of the influence of US media (Friends, Sex in the City, Batman, Superman, Star Wars vs Only Fools and Horses, Upstairs Downstairs, Yes Prime Minister, Eastenders, Dad's Army) on English language programming consumption.