Gus N' Bru is a fictional label of Canadian whisky that is the preferred liquor of the Hicks on Letterkenny.
The label reads Gus N' Bru in stylized letters and drawings of two terriers, presumably the eponymous dogs. Official merchandise featuring the label, as well as promotional copy for the May 2018 "pup-up" shop in Toronto, names it Gus N' Bruno. "Gus" is known to be the real-life dog of Jared Keeso, a pit bull mix. No explanation has been given on the show for the similar appearance of the dog on the label with Wayne's dog Gus, but one may surmise that in-universe, Wayne named his dog after the dog featured on his favourite drink.
Gus N' Bru is a staple of the town, with the Hicks and the hockey players frequently seen doing shots or taking slugs of it. It was introduced on the show much earlier than the other popular alcohol, Puppers lager, appearing in the very first episode. Gail pours shots for the Hicks when they come into MoDean's, then takes a swig of it herself; the bottle is turned so that the label is clearly visible (Ain't No Reason to Get Excited).
While a Puppers beer brewed by Stack Brewing has been made available to the public, albeit for limited runs, no retail variety of Gus N' Bru is sold. Lisa Codrington and Kamilla Kowal (Bonnie McMurray) poured samples of "Gus N’ Bruno" at the May 18, 2018 "pup-up" shop in Toronto, and plans for distribution through the LCBO seem to have existed, only to be scrapped. A May 31, 2018 tweet from the official @LetterkennyProb account stated that they were working on it, but there has been no followup since.
Whisky, an alcoholic spirit made from grain mash, is spelled whiskey in Ireland and the United States and whisky elsewhere in the world, for historical reasons. In Canada, "rye whisky" is defined by law to be the same as "Canadian whisky," regardless of whether it is actually made with any rye, again for historical reasons (in contrast, American rye whiskey must be made from mash that is 51% rye grain). Most Canadian whisky is made from corn (maize) or wheat mash, and blended with whisky made from rye mash for colour and flavour.
Gus N' Bru is known to be sold in different sizes and varieties; at Wayne and Katy's Christmas party, "Gus N' Bru Gold" is the "main event," the shot to be taken at midnight (The Three Wise Men). In Quebec, a very similar-looking label is seen for the local whisky canadien, Guy & Bruce, with the same style of lettering but featuring sketches of two cats instead of two dogs.