Bonjour,
Yes your stock photography earnings (from all countries) should be part of your other earnings. At least that's the tax advice that I was given by my tax professional. I received T5 from the Canadian companies (i.e., Canstock) and I got my W-8 forms from the US companies. I declared all of these as part of my revenues.
My photo business is registered with the CRA, so I was then able to claim expenses to help offset the revenues (i.e., home studio and other shoot and travel expenses).
Cheers,