Favor and favour are two spellings of the same noun or verb. The spelling depends on the type of English.
In American English, you use “favor.”
In British English, you use “favour.”
Canadian English mainly follows British English guidelines, so favour is the correct spelling.
The same distinction applies to similar words, such as “honor or honour,” “labor or labour,” “favorite or favourite,” “behavior or behaviour,” “color or colour,” and “humor or humour.”
It’s important to choose one type of English and use it consistently. The QuillBot Grammar Checker can help you with this.