Look, lying to Immigration officer was usually not a good idea, but sometimes you got to take the chance.
If you tell them the truth about your off-stay in US, you won't get your TN for sure. So this is one of the rare situation where you must take a chance.
Think it that way: for a Canadian citizen, what's good about US except working there ? If you can't get TN, then US is no use for you, so why you care about "不良記錄" ?