I'm building out the fields and sync between Eloqua and Salesforce as well. I'm curious about any examples of processes that people have created.
My initial thought is that I'm going to have a unique opt in/out field for Canada leads and contacts and the field must be filled in if the country field is Canada or (blank). Since you can't assume where a person is located if their Country field is blank. And if the value changes then time stamp the change.
I also have to setup a process for leads/contacts in Germany and a few other countries because we're growing into those markets. If someone has a good multi-country process I'd be interested to hear what they do.