Hey I guess that by now you should be really locked on your destination. If not, you get plenty of advices so I ain't gonna add my idea.
About winter biking; well, it's sucks. But it's also doable.
I'll spare the gear nececseties (I misspelled that) cause you got plenty of info and will emphasize the mental aspect. The sun rarely comes (I once counted 14 days in northern Ontario. 14 with no sun) and that has a mental challenge of urself. It's always gray.
There's always this weird rain-ish that is kinda like hail sprinkles and so you will always be wet and therefore, cold (and sleep uncomfortably ofcourse).
The scenery is not as amazing, since it's always cloudy.
THE MORNINGS. Time to wake up. You can have the best gear in the world, but everyday (or most days, as there aren't many active hosts along the way) you will have to leave your warm -9999 sleeping bag and 5 season tent. That to itself is extremely hard and dissing. You look at the watch, it's 09:30 am and still dark. But you gotta start the day, even if it's fuckin 15F outside. Sun sets at 4:30~ pm.
Some photos from Montreal-Vancouver (biking with some hitchhiking pickup trucks) and from Vancouver-Whitehorse in January, hitchhiking.
The picture in the dark if the van was taken at 9:30 am.
In one of the pictures with my bike in a steep climb, my water bottle froze the next morning. Could t drink.
Thoughts about that emergency blanket: it's horrible. All your sweat will gather. Impossible to sleep well with it.
Also I've added a long stretch of borring flat road with no sun and living soul for a 100 miles (and that's not a small info stand).
It can really get in your mind.
Not trying to spook you, just to give a better understanding of what it feels like. The gear sure, have good gear, but these are the real challenges you'll face, and many more.