There are several. A good starting point, depending on your budget, would be VIA Rail themselves: VIA Rail Canada: Enjoy great discounts on our best fares, today only!
. There are also a number of other packagers that feature VIA trips. Google "VIA Rail vacations" to find a whole list. If you have the money and want luxury, consider Rocky Mountaineer - also sold directly and through other travel sites. As with packages offered by airlines, few of these will be less expensive that something you can put together yourself, but I understand the attraction and convenience.