Three separate driver downloads are available, each targeting a specific manufacturer: Canon, FujiXerox, and Lexmark. The Canon update, version 2.4.1, is 300.83MB in size and installs and updates drivers for various models. The 2.1 update for FujiXerox printers and scanners is only 45.43MB, and the 2.3.1 update for Lexmark printers is 121MB in size.
As always, you can double-check what printer and scanner models are officially supported by Snow Leopard by scanning through Apple’s Knowledge Base article on the subject. Printers are sorted by model.