Hi and welcome, Kathleen!!
In terms of strictly Canadian websites, check out Addition-elle: http://www.additionelle.com. That site allows you to browse three plus-size collections at one time, and you can sort in a variety of ways. There are plenty of brick and mortor stores around too, depending on where you live.
Failing that, you can always go abroad if you're willing to pay shipping fees. Nordstrom has an unbeatable online dress selection, and they do deliver here: http://www.nordstrom.com
Hope that gives you a bit of a start. I'll search my brain for other options.
