Actual furnace fans aren't that loud, or they wouldn't be tolerated in homes. Why don't you try to find a trashed furnace and salvage the fan out of it to see how it does? It can't be worse than the plastic box fans, and can be ducted way easier.
When I suggested a furnace/AC fan this is exactly what I had in mind. Sure there would be some fabrication required to fit the fan(s) to you application, but they can move a lot of air quietly. If the one(s) you find are new enough they might have built-in speed control easily manipulated by an Arduino or other microcontroller. If it's an older model you can find fan speed controls for not too much money.
Given that it's gotten cold in Canada I'll bet that the furnace/heating shops probably have some, or can get you some pretty quickly.