Ella, all I can say is that I'm not planning on querying Canadian agents, at least not in the beginning. The US is a much bigger market and I figure American agents are going to have better contacts. Besides, if I understand correctly US/Canadian rights are sold as a unit. Having said that, I'll check Canadian agents out if need be. And I am certainly open to being educated by someone more knowledgeable if I'm out to lunch on this.
Well, I wouldn't say "out to lunch"...
I think, typically, that if a US agent is selling rights, then yes, US/Canada rights are sometimes sold as a unit. I think this is much more rare if a Canadian agent is selling rights - in that case, I think they tend to break up the markets, which, to my mind and experience, is an advantage (I think it's beneficial to have a separate Canadian contract, rather than having Canada included as a pretty-much no-cost add-on to the US contract). As far as connections go, any Canadian agent worth their salt will be well-connected in the US, and able to work there quite comfortably.
As far as the best agents in the country go, I'd start at the top with (in no particular order):
Denise Bukowski
Westwood & Associates (John Pearce is a good guy)
The McDermid Agency
Don Sedgewick at TLA
Dean Cooke & his compatriots
Carolyn Swayze