It may be pronounced either way, and may also be spelled “broach”, an alternate spelling which is very common although probably slightly less than this chart implies given multiple meanings of “broach”.

I’m not really informed on this history of this word, but I think it’s possible that the “brooch” spelling increased in frequency along with the pronunciation that rhymes with “mooch” while people who pronounce it to rhyme with “roach” are more likely to spell it as “broach”.