of Qc separation is very low. For one thing, there's no guarantee that Quebec would be able to hold on to its Grand Nord; the vast majority of the people that live there are Cree, and they've already stated they would not be interested in remaining within an independent Quebec, many times over many years.
As for the Maritime provinces... I think it's highly unlikely that they'd be willing to consider joining the US. For one thing, periphery states don't do so well in the US federation. I could see them deciding to go on alone, but join the US? Not very likely. The likeliest outcome would be continuing to send MPs to the House, with the Grand Nord and Labrador forming the physical connection. If the Quebecois didn't like it, well, it wouldn't be difficult for the Cree to turn off their electricity. It wouldn't take long after that.
Mind you, my take is that the likelihood of any of that coming to pass is slim at best. Marois is spinning cotton candy dreams and I'm pretty sure most of the people there know that. What she's really doing is trying the Republican approach of finding an issue to drive a particular segment of the citizenry to the polls, in the hopes of (in this case) picking up some rural ridings so she can get her majority. My feeling is that she's doing a great job of destroying the separatist movement by splitting them down the fault line of the hard nationalists and the folks that actually care about civil liberties.