I believe that would only happen if the item was improperly declared. I ordered a toy machine gun from the US that was seized by CBSA. It was properly declared, but the CBSA deemed it to be a "replica" and therefore prohibited because it said "replica" on the box. It was about 1/4 the size of a real M16.
Anyway, none of my shipments are ever held up in customs, except for one, which was put in the dangerous goods section in error. It was a chess set - LOL!
That's a good way to get stuff you need deem it to be a dangerous item.