It turns out that it is possible to speak honestly about politics, not pull any punches, and have an open, far ranging conversation. The secret is to not get personal, even about absent persons the other side might have emotional ties to and be willing to let peripheral points go in favor of carrying the main front.
In the end I was even able to learn a bit about Canada's health system and expound on the case against it. This has been, to my experience, the touchiest policy area Canadians have. Mom denied the problem of waiting times, son called it a myth, and then dad spoke up and said he understood what I was talking about. He claimed it to be a problem of inadequate budgets to keep operating rooms running 24/7 that limited surgeons and others from operating to capacity. I said that it sounded similar to what I had heard but that my information was old and would like an update. I let him carry the tale for the most part and it was relatively smooth sailing from there.
Ideologically I will likely remain across the aisle from them. But it is still possible to talk and persuade if personalities are kept out of it.