While I don't agree with what else Danik has said, the part about provincial health care systems is true. Nothing to do with health card expiry. There is really no open information-sharing between most government agencies/departments. Provincial health only knows a person is out of Canada if the person actually tells them. If IRCC wanted information about a person from a provincial health authority, they would need authorization from that person or they would have to submit a formal request. This really only happens when IRCC is investigating fraud cases.
When I worked at EI, routinely files would be reassessed when the system would pickup that applicants were out of the country on vacation, when they said they were looking for work
ESDC knows when a person has been out of the country and when they arrived back because that information is sent to them from the CBSA
It says right on the customs card, that this information can be shared with other agencies to enforce policy & laws
It doesn’t specify which Government agency, so I assume everyone
When people sign that form , authorization is given
“ Information from this declaration will be used for CBSA control purposes, and may be shared with other government departments to enforce Canadian laws. For more information see Info Source (ref. no. CBSA PPU 018), at a public library or visit http://infosource.gc.ca.“
People would be genuinely surprised to receive a letter , in effect , that the government knew when they left & returned , and that they owe benefits back
All those cards & information go somewhere
I won’t go into details on how deep the US CBP can dig and get information, and everything is shared