In years past (about 6 times across 2002-2009), A certificate was required, and checked 4 out of 6 times. Since that, in 2013, I got a certificate, and neither agent wanted to see it. In 2014 I checked regs/internet, and just traveled with the rabies certificate. Neither border wanted to see it when I offered it.
canada changes their rules often. The US changes their rule much less frequently, but particular border agents change their focus on the rules as often as canada changes the rules themselves.
I've found it helpful to just print the pages where I found the rules I'm following, and bring them with me. That's worked every time.
Remember that much of the dialog is just to determine if you are attempting to smuggle something.
