I have personally used Uniden Repair during this whole US-Canada trade issue. I did have to pay some duties but I dont remember seeing any tarrifs or tarrif codes on my commercial invoice paperwork.
As far as I am aware, They've never had an issue with a Canadian customer sending an item to their Texas repair facility.
However, please do yourself and favour and use UPS, FedEx, or DHL to send your repair. DO NOT use Canada Post! You will need a PhD to complete thier customs form and other paperwork (which their website constantly refreshes and crashes when trying to fill out their online only form). Canada Post staff have been less than helpfu, but that's another topic altogether.
You might just have to take your lumps and pay the $40-$60 to get your item there via the couriers I mentioned. It's usually there the next day. Turnaround time is usually 14-20 days, sometimes a month if they are backed up or if your repair is delivered on a holiday. Since they moved their repair facility from Roanoke to Flower Mound, I found Uniden has really streamlined the process.
I appreciate you reaching out before sending it via snail mail and having headaches down the road. All the best with your repair.