This question has been asked before on this forum and a poster was going to ask CBSA specifically. The issue is that once you complete immigration/customs formalities you exit into the arrivals hall and then have to go the departures level to checkin for your return flight so in effect you are entering the country. Unlike a connecting flight where you could stay airside in your case the return is a completely separate flight.
Canadian government has also implemented an essential travel poilcy and whilst immigration is on the list of exemptions not clear how they will react to same day or one day soft landings as far as the quarantine rule is concerned. Common sense says it should not be an issue same day but the trouble is that you will always have an individual who says they will checkin straight away but then has time for an excursion outside of the airport so not so easy to police.
Not sure anyone has an answer or of course whether the 14 day rule would be relaxed by May.
As for airlines still running as you may be aware they are, BA for example, parking more and more planes ,potentially laying off pilots/crew so who knows what flights will be flying over next few months if simply not viable load wise. IRCC have published various guidance for people with travel issues but as often usual with IRCC the language often vague as opposed to outright saying anyone with COPR expiring next 3 months do not worry
Not anytime sooner since cases are increasing day by day. And would increase in upcoming days, 14 days isolation policy wont be taken back unless Covid is completely eliminated. This is quite obvious and one shouldn't have second thoughts about it.