For Clarification Given Topic Title:
Canadian citizens have a Charter right to enter Canada. Citizens cannot be denied entry. So there is no question about whether a citizen can "enter" Canada using a foreign passport. Any means of verifying identity will suffice for a citizen to obtain "entry" into Canada.
As the other responses addressed, the practical question is whether a Canadian citizen will be allowed to board a flight headed to Canada.
Cursor18 mentioned a special authorization, which i thought i can apply online within 10 days of entry to Canada.
As the IRCC information provided as linked above by
@cursor18 indicates, having a valid visa-exempt passport should enable the new citizen to obtain ELECTRONIC authorization to board a flight to Canada. Contrary to the post by
@PMM this does not involve the Canadian consulate abroad. HOWEVER, this cannot be applied for prior to becoming a citizen (and can only be applied for within a ten day window of the planned travel date back to Canada). And given the lack of reporting about how well this actually works (especially given the precise details in required fields in the application, noting this is clearly an electronically processed application so any flaw entails high risk of not getting the authorization), in conjunction with being a brand new a citizen (thus depending on the GCMS records to be updated rather promptly following the oath ceremony), hard to offer much if any reassurance about how well this will work in practice. The downside is that if the electronic authorization (which appears to be very similar to eTA but special for citizens and for a very limited period of authorization) does not work, then the local Canadian consulate will be involved and the caution expressed by
@PMM looms large.
And given that it is Cuba, there is no travel via the U.S. alternative (except for some creative and probably expensive flight routes).
I am not familiar with what
@charmainefrances describes. Seems good but it also seems at least a bit incongruous with what is otherwise known.