I have a trusted traveller interview coming up and I received a pardon about 10 years ago so my question is…. if I get asked about ever being arrested at this interview what should my answer be? And would I need a US Waiver?

We do not know what the Americans can see but usually they look at the RCMP file which will be blank if you have been pardoned.  You do not need a US Waiver since you have not been denied entry however the risk that you run by answering these questions with the Americans is that they can flag you about having a pardoned criminal record which may result in not only being denied the Nexus but also possibly being denied entry to the US which would then require a US Entry Waiver or I-194.