It looks like everybody's on board with the storm happening. The snow that Ottawa will be getting will likely start Thursday evening with the main dump happening Friday morning. This snow will be from the northern jet stream clipper-like feature. A note of caution: there is a chance that a mere 50km shift south in the storm track and we get virtually nothing. I doubt that will be the case. A more likely scenario would see a shift northward, giving Ottawa more snow.
Once the clipper feature is past Ontario, it will phase/merge with the southern jet stream feature and "bomb out" along the coast of New England. Areas from New York to Maine will get inches to feet of snow. The Maritimes will get blasted Friday evening into Saturday, not that you would know from the Env Canada forecast right now.
Snowmap courtesy of Accuweather. It's conservative, ie on the low side, in my thinking.