You should fax or mail the Buffalo office a letter stating that you want to cancel your application. Make sure you include the file number. Their contact info is here:
http://www.cic.gc.ca/english/information/offices/missions/buffalo.aspIf your wife lands as a PR, you are responsible for her financially for 3 years after she lands. If she takes social assistance or even disability during this time, the government will send you the bill. Maybe you can dodge their bills if you stay in the US but I am sure, like other government debts, that they will never write this off so when you return to Canada, you will have to pay.