We just had this conversation with an immigration lawyer, acquaintance wants to travel with us in the spring and we would be arriving in the US by boat.
He is now 32, was charged with marijuana possession at 19 and not convicted. Charge was dismissed .The charge shows on his file and will not go away.
Its pretty much at the discretion of the US border service guard how they handle questioning and once declined you get sent back on the spot.
He got this wrong once, at the ft Erie bridge was asked if he had ever been charged with a criminal offence in Canada, he said NO, they repeated the question and he again answered NO, they stated " you are denied entry to the USA today, you will be returned to Canada please accompany the officer that is approaching" , he said I WASNT CONVICTED, and they said " that was not the question asked".
He hasn't been back since, little nervous about the process. Would be very awkward for all involved if he got booted again.
Moral; never lie to these guys