I live 25 miles south of Burlington, VT and I frequently go to Montreal. I plan on 2.5 hours from here, so 2 hours from Burlington. Your variables are time of day, day of the week, and any criminal issues in your past. These variables can cost you an extra 30-45 minutes.
Coming back is easy. By the time the show is over and you leave Montreal you get to the border around 12:30-1am. The guards are typically grumpy, but they process you through quickly.
I have never been over the crossing at Champlain NY, but I have been over Rousse's Point. This crossing is smaller and sometimes quicker.
I have been making this trip for almost eighteen years and I have seen many different scenarios. UVM is a great school and Montreal is the METAL capital of North America!!
" Capitalist by Day, Anarchist by night! "