While it is true that Alexander Keith's India Pale Ale (and Keith's Light) are only brewed in one brewery in Halifax, Nova Scotia, it is not brewed at the Alexander Keith's brewery on Lower Water street. (Also known as the brewery market.) That brewery simply does not have the capacity to brew that much beer. A large volume of Keith's is sent to Ontario where it's sold as an import. Keith's IPA is brewed exclusively at the Oland Brewery, in the north end, on the corner of Young and Agricola streets. The Oland Brewery is owned by Labatt's, which in turn is owned by Interbrew SA.
The Keith's brewery does make some limited production specialty brews, such as Celebration Ale and Honey Brown Ale, but it is more of a museum than a working brewery.
To note: The Keith's Brewery pub is open on Sundays, due to it's historical significance for tourists.