、。
If he were to hear about your marriage, he'd be furious.
Literal
By-chance he [subject-が] your marriage's matter [object-を] listen-[if-ものなら], he [topic-は] tremendously will-be-angry [probably-だろう].
~ようものなら is a conditional expressing an extreme, unwelcome hypothetical — 'if X were to happen (which would be terrible).' 聞こう is the volitional/hypothetical form; combined with ものなら it conveys 'should he even attempt to hear.' A literary/dramatic conditional with stronger emotional stakes than plain ~たら.