A bus only has one driver. He has to sit up front and drive. He does not have the time to mind the health of his passengers. A passenger would have to be in very bad shape before anyone said that someone onboard was severely ill or dying.
We would need a link or a mechanism to take care of persons who are found to be seriously ill on trains. If a passenger is found to be seriously ill, his case could be reported to the Public Health Agency of Canada, describing his symptoms, and so on. to ensure that the person is taken to a place where he can undergo diagnosis. I think that such a procedure would be good.
Nonetheless, if a passenger is seriously ill at the border, there may not be adequate facilities to perform a diagnosis. It would require physicians and other resources such as tests.
It would also depend on the type of problem. If someone comes down with a fever caused by the Ebola virus, it is obvious that he is seriously ill. He might not even get into the country alive. If he gets in, he will really be in bad shape because the disease has gone beyond the incubation stage. Rapid transportation does not leave enough time for incubation to take place during a trip.
I think that in any case, there will be have to be a diagnosis along with specialized care. There is already a system in place, because the Public Health Agency of Canada is in charge of infectious disease prevention and control for the entire country.