Lake Champlain is a great lake to sail on, I love the scenery.
As far as your trip, you should take the mast down as said above on the Hudson and head up the Champlain Canal. Lock 12 Marina (Whitehall) is right at the end of the canal can restep your mast. Bouy 39 Marina (Vermont) also has crane. I've never used either of these services there, so call ahead for prices, etc. There are also many places up the lake to step the mast, but you mine as well all the time possible with your sailing guru.
Also, if you go as early as stated, the Champlain Bridge at Crown Point which was just blown up is a "do not enter" zone till April 15th (I know its still winter). Just check ahead to make sure that you can get through there and if there are any issues related to that. I'm sure there will be some activity there and its quite narrow.
Now as far as the Champlain Canal goes, check out Champlain Canal
to get tons of info for that part of the trip. I'd suggest not getting there before opening day, and I would suggest against stopping at Fort Edward Yacht Basin with such a large boat/mast. Also note the short operating hours during May, its going to take at least two days to get through the Champlain Canal. I'd suggest day one stopping at either Mechanicville or Schuylerville and going as far as possible on the second day.
Let me know if you have questions.