Apparently the rule in English is, to turn a verb into a "one who verbs" noun, add the E R suffix if the verb ends in a single consonant: V E R B E R, one who verbs. There are other rules for E R versus O R, none of which apply here. A R can be used for this purpose, but is much more commonly used to adjective nouns: spectacle, spectacular. I do not know the rules in French, but the verb we are attempting to noun here is probably more M I R A C U L something than M I R A C L E.