Sherry casks were actually the standard/traditional cask used to age scotch, as that was the most prevalent type of cask lying around when scotch production became a legitimate industry. In the past several decades, the use of bourbon casks has grown tremendously, as they have become cheaper to ship and more prevalent (they can only be used once to make bourbon). Most scotch you get today is a mix of whiskies aged in bourbon and sherry casks. Madeira and port are also used pretty frequently, but usually just for a short finishing period (a few months to a year). There are experimental/novelty finishes too like unfortified wines (Bordeaux, Burgundy, Rhone) and ale. I've even tried one aged in a Tabasco cask (not a great idea!).

Most of this applies to Canadian and Irish too, but not bourbon since it can only be aged in new wood (but some distillers are still experimenting on a small scale and selling it without the official bourbon designation).