As the sponsor, recommend you apply from within Canada if you reside in Canada.
-if you're a PR, you MUST apply from within Canada.
-if you're a citizen, they may end up asking for additional stuff (intent to return to Canada) if applying from abroad. (Applying from outside although resident in Canada might trigger these additional requests, but might not. Why risk it?)
If you're a PR, you can do 'short trips' abroad while in process. If you're a citizen, no issue - although long absences might trigger the bits above (probably not unless clearly not living in Canada).