You don't have to name names, but do you have any "horror stories" of jobs gone awry?

Just ones where the client never pays. Most often I require a deposit after a certain amount of work has been done, usually 35%. Sometimes I will go through the entire commission before requesting money, as a kind gesture. The white knight syndrome does not bode well for artists though, lol. All this said, the larger companies always pay. It's the small freelance work that you have to be concern about.

Do you think that your work has had more exposure because of work done for American companies ?

Not necessarily. I think it does depend on the property you are working on, but there are plenty of good Canadian and American IPs.
 

Is your nationality is usually attached to your artwork that gets
published? Does artist nationality matter to you?

In bios I occassionaly state where I live, usually in publish books. I would actually prefer to keep my location private. With the internet, it doesn't matter where you live anymore.
 

Any final comments?

Working with both Canadian and Amercian companies will give you more opportunities in the long run. As long as you keep the ethics in mind and deliever on dates, then any artist will have a long run in the business.