I once had a longish layover at YVR so I asked the agent whey she was asking me the purpose of entering Canada. She said it was to judge the risk that I was carrying contraband. Which, actually seems like a pretty reasonable point. If I don't have any reason to visit that I can tell them then presumably I have a reason I can't tell them... The only problem is that as a Canadian it's pretty easy to just say "to visit friends and family" so I'm not sure how useful it is in practice. I can't imagine they care about health care access -- I suspect they wouldn't do anything even if you said that was exactly what you were doing.