YUL - No problems.
YYZ - No Problems.
YYC - Got pulled over for my first secondary last month returning from PHX with my family. I thought at first it was because I declared 2 60 oz bottles of Tequila, which is over the limit. But it was to ask my 7 yr old daughter questions, such as are these your parents. She was travelling on her own passport as well. It didn't really bother me as it took about 1 min, and they didn't make me pay extra for the booze!

As far as using the US pre-clearance, I find it very inconsistent. They either ask many questions, probing into your personal life, or they scan your passport and don't ask you anything at all. Last weekend I was able to enter using nothing but my drivers license.