I've been here since 1995, and have renewed 18 times, always at YVR. Approximately 20-30% of the time I run into a guy taking that position with me. (100% male TN inspectors over 17 years - that's some weird gender bias in a job which really doesn't have any particular need for men vs women) Sometimes, they go so far as to say, "I don't think there's anything temporary about your stay, you're planning on renewing again next year, right?" [note - I love how they try to close me on that. ]
Regardless of what they say, you always calmly reply with the following mantra, "My period of employment is for a period of up to 3 years [note: used to be one year]", at which point my plan is to return home to Canada.
Every statement you make with immigration must be some variant of that, and you must never, ever, suggest that there is the slightest thought/plan of staying past your limited visa, even if you plan to do that by re-applying.
With the exception of the first couple years (where I was rejected twice), I've never had to spend more than 10 minutes at immigration. I will admit the confrontational attitude does get your heart racing...