Q. As far as agent seeking goes, should one seek out different agents to represent interests in Canada and the U.S. (just as you'd have one agent for novels and another for the screen) or is one all you should worry about? I'm thinking primarily of features now.
I have an agent for Quebec only, and agents for the rest of the world.
Generally US agents will not like your carving out Canada for your Canadian agent, because they can at least negotiate those deals for you even if they will generally not find them for you. And they want the 10%. Some have policies about no dual representation. In the case of Quebec, it is such an idiosyncratic little market, no one can convince me they can rep me here from Toronto. And all policies can be broken if there is a strong enough financial incentive. The stronger your career is, the more people will make exceptions for you.
Get the local (Quebec, Canada) agent first and then try to hold onto them when you go looking for worldwide (Toronto, LA) representation. It's easier to get a fait accompli accepted.
At some point I might change Toronto to LA (though my current Toronto agents are doing their best to hustle in LA), but I'd still try to keep Quebec, er, sovereign. Just as all politics are local, all selling is local.