Seriously, there’s no way the Northlander, as planned, would serve the people headed to their cottages the way remote VIA services do. It won’t stop just anywhere en route, unlike The Canadian in Northern Ontario or the White River RDC. Within cottage country, it will stop in the town centres of places like Gravenhurst or Bracebridge.
The Muskoka cottage country area is not the kind of market that will take trains anyway. If you have a cottage, you probably also have a SUV. They all have road access. Any cottage-goers taking the train will be visitors or family members being picked up at the nearest station, not talking big loads of baggage.
The old Northlander, if I recall, didn’t have a baggage car either.
The only thing I see different is Ontario Northland being less anal about the onboard luggage allowance than VIA is.