Maranta leuconeura kerchoveana, to be specific. I 'think' that this one might be easier to grow than some of the other Maranta. Commonly called Ten Commandments plant.

Amy, the only other thing in that bed that would get that tall would the the aretemesia, and that is not what that is..............could it possibly be just a weed???

You might want to ask on "name that plant."

Difference between nighttime and daytime temps shouldn't be problem; even 20's is pretty warm (I am assuming that is C). My daytimes are in 30'ties C, and nights drop to 12*C sometimes - I wouldn't mind if that was every night! :) Cooler nights are actually pretty good for plants. I am north of Toronto, On, and weather is quite similar to yours in Montreal. Pls. do not use sand for potted succulents regarding what you read on some 'blogs'. Yes, it could be used for some, but only if you really know your plants. It is best if you just don't use it. Grit is great addition or pumice; but if you don't have (or not easy available), use lots of coarse perlite. If you mix perlite 50/50 with the Cactus & Succulent soil, that will be quite an improvement. If you can, keep plants outside. But make sure you acclimatize it very slowly, since it is very etiolated and most like very weak. You need to get it into better light and water properly - sparsely is not proper for succulents. If you pot it into well draining mix, you can water thoroughly when needed. Pot seems to be very large for your plant. I would repot it into smaller pot. Etiolated plant will not 'revert' even if you give it much better conditions. If my plant, I would trim/prune it extensively. If you want some ideas, pls. ask. BTW, here is Cacti and Succulents Forum if you are interested to read more about succulents...