#420983 is a caboose used on the M of W trains. The trailer on the flatcar is either a bunk unit or a kitchen unit that the M of W crews sleep and eat in. You only see them now in Northern Ontario where the rail line is far away from any road. And yes, they are air-conditioned. You can see the air-conditioning on the top of the roof.
If you take a trip on the VIA Budd car from Sudbury to White River, you'll run across a lot of work trains with these units. - both the caboose and the bunk/kitchen cars.