Here are some letters from the Canada Revenue Agency dealing with Article XXI (7) (formerly XXI(6)) of the Canada-US Tax Treaty.
2011 Letter from CRA on Article XXI of the Canada-US Tax Treaty 2011-040840
2010 Letter from CRA on Article XXI of the Canada-US Tax Treaty 2010-0380811E5
2009 Letter from CRA on Article XXI of the Canada-US Tax Treaty 2009-0322801E5
1999 Letter from CRA on Article XXI of the Canada-US Tax Treaty 9924098
1999 Letter from CRA on Article XXI of the Canada-US Tax Treaty 9900795
1996 Newsletter from CRA on Article XXI of the Canada-US Tax Treaty
1991 Letter from CRA on Article XXI of the Canada-US Tax Treaty
1989 Letter from CRA on Article XXI of the Canada-US Tax Treaty 5-8223
