There are some rental companies that will not permit their cars out of the state or out of the country, or charge a premium if they do.
Ensure that the rental company notes on the rental agreement that they authorize you to take the car into Canada. You may be asked by Customs when entering Canada, or when re-entering the US, for this documentation.
The route looks to be quite direct, about 400 miles. From Boston north on I-93 to I-91, north to the Canada / US border. I see that you may have routing options once across the border.
Perhaps you should also post your question in the Boston, MA forum.
The best and most direct way from Boston is to take Interstate 93 north into New Hampshire. In Concord take Intertate 89 west. Just after you cross the Vermont border take Interstate 91 north to Canadian border. After you cross it becomes Canadian route 55. Follow it until you get to Canadian route 20 east, which you will take the rest of the way to Quebec. It is roughly 400 miles and about 7 to 7 and a half hours. Go onto Google maps and keep clicking the New England area until the routes come into view. As I don't know your interests, or how long you want to take, it is hard to say what to stop and see, though I personally don't think there are many major must ee sights along this route. A good half way overnight spot if you are interested would be the Comfort Inn in St. Johnsbury, VT, at the intersection of 89 and 91. Good luck and enjoy!!
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