For US Team donations, send to:
USOF
PO Box 1444,
Forest Park GA 30298
and make note that the money is for the US Team Fund. There's a printable form
here.
As far as I can tell, Team Canada donations should be sent here:
COF
1239 Colgrove Avenue NE
Calgary, Alberta, Canada T2E 5C3
but correct me if I'm wrong!