There's only one company, Greyhound. I don't mind taking the bus. Others hate taking the bus. It's pretty personal.
I use Rome2Rio to see options for travel. It showed there was a MegaBus; so with some research it looks like you can take the Megabus to Burlington VT then switch to Greyhound to get to Montreal. No idea if Megabus is better you might want to post on the Boston forum to see if anyone as use either. https://tinyurl.com/y8d5dyb4
Lots of the McGill uni students take the greyhound, I have heard no major complaints from them. Parts of the drive are very beautiful.
Perfect! Thank you so much everyone!