Mr. Smith's class was canceled because of illness.
Literal
Illness [because-のため] Smith-teacher [possessive-の] class [topic-は] cancellation [to-に] became.
中止になった uses になる to express 'became canceled' — framing the cancellation as an outcome rather than someone's decision. スミス先生 uses the title 先生 after a foreign name. A natural school/work announcement.