Advice sought on sending a preamp from Canada to the US for repair and return

I live in Canada and I need to send a high-end preamp back to its US manufacturer for repair and return. I am concerned that on return to Canada it will be treated as a new importation and attract substantial duties and taxes based on its declared value — which needs to be accurate so that I can get the right insurance coverage in the event of loss or damage while in transit. The Canadian regulations are indecipherable (to me) so I’m wondering if any Canadians on the forum has done this successfully and if they could outline step by step the process — eg. How did they evidence the fact that the item was shipped to the US for repair in the first place and is being returned to Canada? I’m at my wits end so any advice would be greatly appreciated!