When I bought mine I picked up some temp tags for it, I just had to show proof of insurance and possibly a safety inspection (can't really remember). However, that was in Ontario; not entirely sure what the procedure would be in Quebec. Without registering it here I'm wondering if you'd have to get the temp stickers from your local DMV?
I'll put a thread up on the local Subie forum and see if anyone there can help out.
Edit: Tada!
http://www.ottawasubaru.com/forum/vi...hp?f=1&t=33768
Also, a quick bit of searching indicated that when bringing a car into Canada from the US we would have to get a trip permit from a local authority. This leads me to think that you'll need a Maryland issued temporary tag to drive the car back down. I don't see driving around here with it being an issue as long as you're within the allotted time of the permit.