As stated by the director of the CDC in the press conference, all air passengers departing the affected countries are screened for fever. Fever is most often the first symptoms present, and therefore you can logically believe that if the passenger left Liberia and is on a plane, he does not have Ebola (or is not symptomatic for Ebola). Therefore I would be fine sitting beside him.
Europe isn't an affected area. No one on my flight from London was checked. It certainly wouldn't be hard to get from Liberia to Europe with no fever, and then board a plane with fever and sweats.
I can speak to the Canadian process. Public Health Agency of Canada is stationed at all major airports and screen passengers that trips originate in an affected country. We had a suspect patient that had arrived from Germany that begin in Nigeria. Due to the routing, they were screened here when they landed in Canada.
Theoretically someone could fly from an affected country to Europe. Spend a few days and book another trip to North America and not be screened. However triage process in hospitals is that patients with fever greater than 38.6C are asked if they have spent any time in an Ebola affected country within the past 21 days (high end of incubation period).
