The answer is in the Guide 3900:
If I live outside Canada, may I sponsor?
If you are a Canadian citizen, you may sponsor a spouse, a common-law partner or conjugal partner, or a dependent child who has no children of his or her own. However, you must demonstrate that you will live in Canada when the sponsored person becomes a permanent resident.
Note: Permanent residents residing abroad may not sponsor from outside of Canada. Canadian citizens traveling as tourists are not considered to be residing abroad.So there. Canadian Citizens living outside Canada are eligible to sponsor from outside Canada. In fact, just this morning, Ms. Melba Umanito got her Permanent Resident Visa via Family Class Sponsorship.
When we filed her application, her Canadian husband was working in Mexico. She on the other hand was in the Philippines. With proper documentation, her application was approved in no time. Well, there's a slight delay due to Police Certificate from Mexico but other than that, it was a smooth processing.
She will be moving to Canada before the end of this month.