-- Last Updated: Mar-12-13 10:55 PM EST --
I have been very happy with the quality of MEC bags having just bought two for my kids. I only have experience with the down ones though but I assume the quality would be the same with synthetic. If you get opposite side zippers apparently they will zip together. They also provide a packed volume size in the descriptions. Happy Shopping.
http://www.mec.ca/AST/ShopMEC/SleepingBags/SyntheticBarrelBags.jsp
Edit, hopefully the barrel bags are rectangular enough.