There are rumours of a new Nexus device in the fall to coincide with the launch of Ice Cream Sandwich. It might be worth waiting for if you get into late August/early September anyway.
However, while it seems very likely, there are no guarantees it will come with the AWS band, and it likely won't come to Canada until February, so you'll have to drive to the US to get it.
Traditionally, Google has had a partner release a flagship device with a major new Android release (HTC G1 for 1.5, Motorola Droid for 2.0, and Motorola Xoom for 3.0), so we may see a partner device with Ice Cream Sandwich and then a Nexus device a couple of months later. That said, they launched Gingerbread exclusively on the Nexus S, so maybe that's the direction they'll go with Ice Cream Sandwich too.
The only thing I'm really confident about is that if something comes up, you'll have to get it in the US. I'd suggest you plan to go with the Nexus S for now, if you get the deal you want. When you're ready to pull the trigger, check back and see if there's any more substantiated rumours of imminent devices.