There are some companies that "host" American shipping addresses for Canadians. My parents use I think its UPS shipping service in Buffalo or whatever, they pay a certain amount for some type of P.O Box, if there is something that only ships to the US they have it sent there and from there UPS will either ship the parcel on to them, or they can go pick it up (for them its only about a 20 minute drive to cross the border).
If your cousins are in Ottawa maybe there is somewhere you can ship it to one of those New York border towns closer to Ottawa and they can go pick it up. Depends how badly they want their See's lol