I don't know if wine merchants still broach the cask in 2021, but why would they? Aren't casks manufactured with a spigot that a seller can just turn on, as shown below? I embolded the phrase below.
Broker has no connection with the past tense of break. It comes from Anglo- Norman brocour ‘small trader’, but its ultimate origin is not clear. A variant Anglo-Norman form abrocour has fuelled speculation as to a link with Spanish alboroque ‘sealing of a bargain’ and Portuguese alborcar ‘barter’, which are presumably of Arabic origin (the al- representing the Arabic definite article); but other etymologists have sought to link the word with broach, as if the underlying sense were ‘someone who sells wine from [that is, by broaching] the cask’, and hence any ‘retailer’.
Word Origins (2005 2e) by John Ayto. p 77 Left column.