HA! Too funny... I only had ONE Carrier quote, another was a Bryant. To be totally honest, I had one quote for a 115,000btu furnace and all the rest were 100,000.
Have they shown you a print out of the Manual-J (Load calc)? They measure each room, walls, windows, and attic? If your old one was 100k, sounds like they just matched what was already in the home itself.
Hopefully they used vanes in the return drop where it connects to the air filter.
Power humidifiers, don't work real well installed on the return.
In order to add moisture to the air, they need heat. And there isn't a lot of heat in the return air.
As others have said, pump up under the outdoor unit would be nice to protect it against snow accumilation.
Canvas would be nice, and is actually a code. But may not be enforced in your area.
Other then the humidifier on the return drop, and no pump ups under the outdoor unit, I didn't see anything terible.