Regarding whether USco (a US C-Corp and a “qualifying person” for purposes of the Canada-US Treaty) would be considered to be carrying on business in Canada by virtue only of some of its employees being Canadian residents who worked from their homes for two or three days a week, CRA noted:
[S]hould the Canadian resident employees of USco act in a product development role, their activities may bring USco within the extended meaning of carrying on business in Canada under the Act. For example, paragraph 253(a) may be applicable if the product development role amounts to “creating or improving, in whole or in part, anything in Canada”.