Can a 10' high wall be built with 2x4's in Ontario?
The national building code of Canada specify's exterior walls must be framed with 2x6 or 2x8. Interior non load bearing may be framed with 2x4. 
I hope this helps. 

https://www.saskatoon.ca/sites/default/files/documents/community-services/building-standards/tall_walls.pdf