I have gone to Canada 6 times so far - 4 times as a PR and 2 times as a USC. Crossing a border in either status was always a hassle-free procedure for me. Canadian border guards were not as consistent as their US colleagues: two times they did not even open my foreign passport or look at the GC, two other times they actually examined my passport and my green card, and two last times they typed all information from my US passport card and US passport book. Americans, on the other hand, always asked the same questions and always scanned the immigration documents. My last experience is described in one of the threads.
As for passport card vs passport book when travelling to Canada - it all depends. If you don't anticipate any emergency that will make you fly from Canada to your native country, then passport card should be OK. I usually make short trips (4-6 days) to Canada and I always drive by car, so in my case passport card will suffice.