i always travel with my gifts already wrapped and carry extra wrapping paper and cellotape in case the gifts are opened....
i do that both going into the US and into Canada...
so far i've never had anything opened....
by the way, when entering the US, non-residents don't have to declare anything that they're not leaving in the US....so if the gifts are for your own family and you're taking them out of the country again with you, you don't have to declare their value...