Hey there. I'm also from DC originally. I ditto everything written above, especially the part about staying out of Prince George's County (the most dangerous area to live in the DC area, HIGH crime rate per capita, even worse than southeast DC). Traffic is a nightmare in the entire DC area and I don't miss it one bit.
That said: Gaithersburg is about as exciting as watching paint dry. And it's much more a DC suburb (closer) than of Baltimore. On the plus side, you are very close to DC and Bethesda for your fix of nighlife, culture, entertainment, etc.
If you have the choice, I'd go for Montreal!