What do you mean by mountain multi pitch?
If its an alpine setting you want then the only ones that come to mind are
Cannon Cliff New Hampshire (rock and ice)
Stuff in Huntington ravine Mt Washington NH (rock and ice)
Mt Katadhin Maine, (rock and ice)
Quebec would have some but mostly in the Aid climbing Cap Trinite, not really alpine, mostly marine
A better place to start would be multipitch climb at a crag ie short approach, cathedral in North Conway for example.
Bar Harbor Maine is a good spot, I highly recommend "Story of O". Its close to F'ton so makes a nice weekend. Precipice in Bar Harbour is a good area, there is a whole bunch of multipitch route ranging from 5.6 to hard.
If you want to get your multipitch systems down then the Gunks in New York is a awesome place. There is so many routes jammed together that you can do easily 12-18 pitch a day (not a weekend day but a midweek day). YOu really want to be efficient if you do an alpine route.