Main Difference

The main difference between Cancelation and Cancellation is that the Cancelation is a alternative spelling of cancellation and Cancellation is the act, process, or result of canceling; as, the cansellation of certain words in a contract, or of the contract itself.

Cancelation (noun)
alternative spelling of cancellation

Cancellation (noun)
The act, process, or result of cancelling; as, the cancellation of certain words in a contract, or of the contract itself.
Cancellation (noun)
The operation of striking out common factors, in both the dividend and divisor.
Cancellation (noun)
A postmark that marks a postage stamp so as to prevent its reuse.
Cancellation (noun)
In United States intellectual property law, a proceeding in which an interested party seeks to cancel the registration of a trademark or patent.

Wiktionary

Cancellation (noun)
the action of cancelling something
"the project was threatened with cancellation by the government"
"the show is sold out, but check for cancellations"
Cancellation (noun)
a crossing out of something written
"all cancellations on documents must be made indelibly"
Cancellation (noun)
a mark made on a postage stamp to show that it has been used
"covers showing stamps and special cancellations"
Cancellation (noun)
the annulling of a legal document
"the debtor can procure cancellation if satisfied within one month"

Oxford Dictionary

Cancellation (noun)
The act, process, or result of canceling; as, the cansellation of certain words in a contract, or of the contract itself.
Cancellation (noun)
The operation of striking out common factors, in both the dividend and divisor.

Webster Dictionary