So someone asked how Andrew is just accepted as an officer by those that know who he really is.
Canada has a combined ranking system. Meaning all Officers from the military branches, Security services and police forces hold Commissions. Should a crisis arise, who is in charge is known off of this system.
As Director General of CSIS Andrew is the highest ranking "Officer" on the Rock. As such, by default, he is commander of the Free Canada forces.
The rank he is using is a cover identity supported by the Royal Navy (Who firmly consider Andrew one of their own after Breach), the acting Commodore title is to reaffirm this authority. Since both the Royal Navy and the Royal Canadian Navy attain their authority from King Charles III, it is the King, ultimately, who grants the Commissions. Ergo, Andrew is in Command and a Commodore.
Hope that clears it up, least for the book purposes.