It is a really good question.
The weight would be about the shipping cost. Customs would be about importing and that would be about the category (jewelry vs. apples) and however Canadian laws value the item. If it is the first item you have imported in years I would think it might be duty free. If you have already imported $10,000 this year I would think it would be super expensive.
I don’t even know what the duties are to import into the United States, but I have come into the US from several countries. I never seem to know what it will cost. Also it seemed to be that there was no duty below $350 in 1971 and it hasn’t changed much in almost 40 years.
Not a good clear answer I know, but I hope it helps a bit.