Hi Simon, second story cob houses are possible for sure, but I wouldn't recommend it for a few reasons. The best way to build cob tall is by tapering and starting the wall very thick at the bottom. To get a true second story you would need to start at 2.5' thick towards the base and taper as you get up. The thicker the base the better in this kind of situation. You also want to make sure your walls have lots of curve to strengthen the walls integrity.
Why is it not a good idea? Nova Scotia is cold, and cob won't do you any good in that type of cold. My first cob house was build in Montana which probably has warmer temps on average than NS and the house was on the cooler side all year. Second, while building cob taller makes for cheaper buildings (roof and foundation costs) the labor involved in getting cob up 10+ feet in the air is a real struggle. If you can do straw bale, go this route or better yet, balecob. Check out my website in my signature to see a balecob house and see if you like it. This house performs much better in the cold, easier to build, and the costs were almost just as low as a normal cob house, but with probably an 1/8th the cob material.