Auto component fitments at a mechanic cross-border in Niagara

Hi.

We are Canadian residents and visiting Niagara Canada for tourism next week. While I'm there, I wanted to take my car across the border for some quick work at a mechanic, which includes fitting some new equipment, like a hitch and a cargo carrier. Do I have to declare these at the border crossing and pay duty on the invoice value while returning. If so, does anyone know what is the duty amount on auto components?

What is the risk in not declaring these. I have a B1/B2 visa for the US. These would already be fitted on the vehicle and it is not going to be lying in the car with new packaging.. so I don't believe a border officer is going to find these are new even if he inspects the vehicle.. I'm hoping.

I'm alright paying duty as long as I know what is the duty value so I can plan for it.