Not sure exactly which yeast "brewers yeast" is, but I use a tiny pack(5g I think?) for 5 gallons, have done several one gallon batches with half packs and the latest one with 1/3 pack per gallon, with great results, so 1/3 cup is ALOT of yeast.
From bulk barn website :"Brewer’s yeast should not be confused with baker’s yeast, which is used to make bread rise. Brewer’s yeast is an inactive yeast, meaning the yeast cells are not live and have no fermentation or leavening power."
The only "brewers yeast" I see is the stuff already listed. There are several baking yeasts shown, but they aren't considered as good for wine or beer as brewers yeast, although technically they would still work.
And there isn't anything terribly wrong with pitching too much yeast in this case. For best flavor the proper amount should be used, but it's better to use too much, usually, than too little. Fermentation ought to be done in a hurry.