As an L-2 spouse he is employment-authorized incident to status and may work for any employer or himself from the immigration standpoint. Whether a US employer or a state requires specific certification to service equipment is a separate, non-immigration question.
Immigration permission is broad; licensing may not be
The L-2 spouse's authorization is one of the reasons families prefer L-1 to TN when the principal could qualify for either. He does not need to apply for a separate employment document to begin work, and his status is evidenced by his admission record showing L-2 spouse status. What families get wrong is assuming that immigration permission answers every question.
A dealership or rental company may require manufacturer certifications, a state may regulate certain inspections, and commercial driving requires a state licence. Those are employer and state matters. Any children under twenty-one may attend school in L-2 status but cannot work, including summer jobs, and each child ages out at twenty-one.
If the year-long placement is extended, the family's L-2 extensions run with hers up to the five-year L-1B maximum. If she instead stays in Canada and supports the dealer remotely, none of this arises, and his employment in Guelph/Eramosa continues unaffected.