How to vista Mont St Michel from Bayeux?

The Google search engine is your friend here. Type in “day tours from Bayeux”. Or “day tour to Mont San Michel from Bayeux”. You will be given several options.

It is an easy drive from Bayeux to MSM. We had a wonderful stay at historic Hotel Lion d’Or in Bayeux where many of the WWII Generals stayed from time to time.

Should we rent a car in Bayeux and drive ourselves?

For Mont St Michel, I used the shuttle offered by the Churchill Hotel. It was very convenient since I was traveling solo and didn’t have a car. I did this back in 2009, but according to their website it appears to still be operating.
http://www.hotel-churchill.fr/en/shuttle-bayeux.html

If the Churchill Hotel is still offering that visit, as Laura's look at their website suggests -- that is the way to do it. Pay them to worry about the logistics, gassing up the van, finding the way, etc etc. It's worth the fee to have them take care of it for you.

Renting a car and driving to Mont St Michel is more difficult and expensive, but would allow you to have time with less crowds in the evening before driving back. We stayed overnight, taking the abbey tour around 4 and then walking around the ramparts and other roads in the evening. You might also be able to take a mudflats walk with a guide in the afternoon, depending on when the tides are (this was mostly a nature experience as a break from museums and history, especially for our 12 and 14 year olds).

And while the train station is at the edge of Bayeux, the walk to the tapestry or cathedral isn't far.

Many hotels h ave shuttles or Viator offers a one day trip from Bayeux.

Viator doesn't run any tours itself; it just lists tours operated by others. Sometimes you pay more by going through Viator. Any commercial day trip to MSM from Bayeux is going to put you there when the place is overrun.

I was happy with the one-day D-Day tour I took. It was operated by Overlord Tours. There are other companies offering tours of the area, and most reports here have been positive. Most of the tours depart from Bayeux, and I believe all of them use vans rather than large buses. That means considerably less time required for loading and unloading the vehicle at each stop. A professional driver/guide will be able to get you to more sites in a day than you'd be able to manage yourself (even with a car), and the background information provided by the guide will be key to understanding the significance of what you're seeing unless your travel party includes a WWII expert.

I recommend taking a packed lunch with you so you can see the sights at your lunch stop (which may be St-Mere-Eglise), rather than having to skip the sights in order to have time for a restaurant meal. You will probably not be permitted to eat in the tour van.

I don't know how early you'll need to book for a late-August tour. It appears that a lot of people are traveling this summer, and tours are likely to sell out in advance. On the other hand, the tour may well be non-refundable if you are unable to go to Bayeux for some reason, so I certainly hope you don't have to book this early.

You might consider cutting your time in Bayeux a day short, renting a car, and spending the night on MSM. August is the busiest time of year at MSM, so any type of day trip will put you right in the thick of the crowds. I really enjoyed getting to MSM in the afternoon, touring the abbey around 4pm, and then enjoying the place as the crowds disappeared. If you consider that an option, I would make sure your room is exposed to the bay so you can cool it off. We were there in June and one of our rooms was in a courtyard without much breeze. It was suffocating with the window closed and just tolerable with it open. Our other room was open to the bay and was very comfortable.