I have noticed the same with �cancel �.
In the online British English dictionary that I just checked, �travelled � is the past tense. (Cambridge)
In the American one, both �traveled � and �travelled � are listed side by side.
I have been told in the past that in some cases (as language natually changes etc) that both can be used for �canceled � and �cancelled �.
I am sorry that this is not a definitive answer.
Perhaps there is not one definitive answer in this (these) case(s).