You don't have to give fingerprints, especially if you are departing from Canada (you will clear the US border at Pearson), but the US Customs personnel do not have to allow you entry into the US, either. So you might be turned away if you refuse.

I don't know if Canadian citizens have to give fingerprints or not. But, if you are not a US citizen, you do not have a 'right' to enter the US. I know that sounds kind of harsh, and I wish the US would do away with its more nonsensical policies like this, but as it stands this is the policy now.