You shouldn't!
MyBandSite.ca was created to be totally complementary to MySpace and Facebook, because let's face it, everyone and their dog is on those two sites. As a band, you are expected to have a MySpace page. But with that said, you are really limited in expressing yourself within their page model. And most MySpace pages are pretty nasty to look at.
If you want to put your best foot forward (especially if you are trying to attract bigger and better gigs, or label A&R folks), you need a more polished calling card, under your own domain, to tell everyone: "hey, we are serious".