“The technology of that time severely limited the number of available channels (broadcast channels being six megahertz wide due to severe interference etc)” is actually very comparable to “the market forces of our time severely limits the number of available distributors (network effects mean everyone is on Facebook and Twitter)”. To a government this is genuinely a strong argument for fairness doctrines.
I personally don’t think the Canadian laws are like fairness doctrines, to me they are more like rent-seeking on valuable Canadian eyeballs, but if the Canadian government does see their laws as something like fairness doctrines, they have a pretty good case for it!
Canada is a pretty small market. Google and Meta have come in and (perhaps unintentionally) destroyed the tiny Canadian news media sector.
I don't think it unreasonable that these companies, (largest on earth), pay a tiny fraction of a percentage of their Canadian revenue to help support that sector.
Without our own news media, we are particularly vulnerable to the toxic influence of American right wing media, billionaire funded astro-turf media and any other foreign entity that wishes to push their agenda.
I personally don’t think the Canadian laws are like fairness doctrines, to me they are more like rent-seeking on valuable Canadian eyeballs, but if the Canadian government does see their laws as something like fairness doctrines, they have a pretty good case for it!