The baseball game was cancelled because of the heavy rain.
Literal
Baseball [gen-の] game [topic-は] severe rain [because-のために] cancel [to-と]-became.
~のために here is the causal 'because of' sense, distinct from the purpose sense ('for the sake of, in order to') the same form can carry. ~となる is the more formal equivalent of ~になる — 'come to be, become.' 中止となる is the set expression for 'be cancelled' in announcements.