The event in Winnipeg was "If Day". There is a lot on the internet about it, for example this wiki page:
https://en.wikipedia.org/wiki/If_Day
And there is this youtube video:
https://www.youtube.com/watch?v=8scLEt70yIE
The event was towards the end of February, which in Winnipeg, is typically extremely cold.
Another good shot of winterization of carriers can be seen in the op-eskimo books. There they built plywood enclosures over the carriers, however it was noted that it resulted in overheating. Hard to heat the driver/gunner position when the entire cooling system is drawing it's air from that area.