Both of these sentences are in passive voice.
To understand the active/passive contrast you must keep in mind that the semantic role and the syntactic role of the constituents are two different things.
In the active voice, the Agent (semantic role) of the verb, the entity which 'performs' the action, is represented by the subject (syntactic role) of the sentence, and the Patient (semantic role) of the verb, the entity which 'undergoes' the action, is represented by the direct object (syntactic role) of the sentence.
[SUBJECTThe organiserAGENT] [VERBhas cancelledVERB] [DIRECT OBJECTtoday's match organiserPatient].
(If you like, you can give distinct names to the verb's semantic and syntactic roles, but that doesn't enter into this matter.)
In the passive voice, the Patient is represented by the subject of the sentence; the verb is recast as a construction with BE + the past/passive participle; and the Agent may be either omitted or expressed as a preposition phrase headed by by. There is no direct object.
[SUBJECTToday's matchPATIENT] [VERBhas been cancelledVERB] optional:[PP[PREPOSITIONby][PrepOBJECTthe organiserAGENT].
The presence or absence of a constituent identifying the Agent does not affect the voice of the sentence: it is passive whether or not the Agent is explicitly named.