I have ventured as far as the Statue of Liberty New York obviously. From Boston you will need to follow the coast south until NY city where you will cut inwards to take the Hudson river, follow this until you reach the Champlain Canal which enters Lake Champlain. Continue on your route where the end of Lake Champlain becomes the Richelieu River and follow this to Sorel where it empties into the St Laurence River, hang a left and Montreal is not very far off.
You will need to make sure boat is in excellent mechanical condition. Find out everything you need to know about importing the boat to Canada or leave it on Lake Champlain until you get this organized.
I am going to say it will take a week to get to Montreal as I assume you will not be up on plane the entire time. I did NY to Lake Champlain in 2 1/2 days however this was with a much smaller boat cruising around 32 mph where I could and at that time gas was $1.25/G. The entire Champlain Canal is limited to 5MPH and will take a really long full day to navigate which is a rather boring day. Nothing special to note except you need to watch out for those ferries in NY which are really bad. The Hudson is full of logs, trees garbage and maybe some dead bodies.
That being said I really enjoyed that trip however the Hudson is not a really good place for going for a dip.