I read a [lengthy] story about a guy from the UK(?) who came here, did some train surfing, and went home. He came back a while later (months, years perhaps) to do a full cross-canada train hopping trip and they detained him at the border and said you can turn around and get on the next flight back to the UK, or come into Canada through customs and promptly be arrested for trespassing. They found a video or some evidence of him and issued a warrant in the months that he was at home in the UK. Cost him his flights to/from as well as all of the logistics, planning and time that went into his hopeful trip.
Be careful out there... CP Rail is one of the few organizations across Canada with their OWN DEDICATED POLICE FORCE. These aren't peace officers or security, they're equivalent to RCMP and can arrest you on site. They're also backed up by a huge national network that SPECIALIZES IN LOGISTICS. Timing, assurance, safety, security and loss prevention. Everyone has radios and they know how to use them. Logistics in Calgary manages most of North America and runs 24/7. There's even a publicly posted snitch hotline at most crossings and yards.
I would love to read stories about your successful endeavours train hopping across Canada, but this is my two cents. Read some threads like
this one for more context.
The risk > the reward, IMO.
Good luck!