Ridden in many states in the US many times with an M2, both over the border and fly-in-and-ride on a rental.
Never been stopped, so not sure about the legality of it or an M1.
If you are pulled over in most states, you just need to show some kind of motorcycle endorsement on your license + valid insurance for your vehicle. I doubt a State Trooper in TX would know the difference between an M1 or M2. As GG mentioned, good luck trying to rent a motorcycle with an M1. Although the popo may not be familiar with a learner's designation on a foreign license, a motorcycle rental agency certainly will.
And if you're riding down to the deep south, you will have to be up-to-date on the laws in every state that you pass through re:foreign learners permit. ie. In TN, state learners permit will only allow you to drive 7 miles from your registered home address. Most applicable motor vehicle acts are state-level not federal, just like in Canada.