All depending from where within the 2 cities you are leaving from and arriving to, it's approximately 600 kilometers or about 6 hours drive.
The flight from Boston, MA to Montreal, Canada is not that long given a flight distance of 251 miles. To fly between these two locations would take about an hour.
About 6 hours.
What is travel time from Boston MA to Montreal by car?
390 miles, about 7 hours
You can plan for a long car trip by booking hotels in advance. You can also plan to stop at National Parks for much needed exercise.
4 to 5 days.
That depends on where the point of origin of your trip is.
4 or 5 hour
One way car rental is certainly possible, although there may be a one-way charge involved. The exact charge depends on the rental location, car size, rental duration etc.
By car about 24 hours
both
Around 18 and half hours.
The drive is around an 1 hour and half to two hours long.
6 Hours at the least.