It's not impossible to travel outside Canada if you are not Canadian. It may be more complicated, depending on the citizenship of the subject, you may have to get some visas, but it's not impossible. I know quite a few people with "complicated" passports who have jobs requiring extensive international travel, but that's not really an insurmountable issue.
If an employee were passed on for a promotion because of their passport, I believe there would be a case for discrimination.
It is totally doable. My work requires me to travel a lot (reason why I've been in the country for over 7 years!! Didn't have enough days until now). And I NEED A FREAKING VISA for every single country... I've been to around 20 or so different countries in the last 3 years...