The 18th century kettle has sloping sides and is not the "corn boiler" type commonly sold. A close copy of an 18th century kettle can be purchased from Crazy Crow Trading Post, PO Box 847, POTTSBORO, TX 75076 USA. English Trade Kettle. Code: 5564-006-000 Cost: $45 us.
One tinsmith suggests that the straight sided kettles were/are late 18th century-19th century.
I am still trying to find accurate information on kettles and canteens. The kettle from Crazy Crow Traders is as far as I can tell from my research so far, a correct type for early to mid 18th century.