In the U.S., the ONLY way to legally transport alcohol in a COMMERCIAL motor vehicle is for it to be on the manifest/BOL as cargo. If it's not on the manifest, it doesn't matter if the container is open, or if the factory seal is intact. Doesn't matter if it's in a cupholder within the driver's reach, or in a toolbox where you need to get out of the vehicle to get at it.
Full trailer of Jack Daniels, to be delivered to the LCBO? No problem - just make sure you have the hazmat placards in place (the alcohol content is high enough for it to be classed as a flammable liquid). Six-pack of beer in the step box (combined step up to the cab/storage box)? You're in a heap of trouble.
People have been nailed when they bought booze at the duty-free before crossing into Canada (less than 1/4 mile of travel before they reach the border, at which point factory-sealed containers not accessible to the driver have the same legal status as in a private car). Bonus points if they didn't "flag" the stop at the duty-free in their log.