The spouse and unmarried children under 21 may hold L-2 status. The spouse is employment-authorized incident to that status; children may study but not work. Each person's own citizenship and age should be recorded because they affect the process and the end date.
Practical points for a short posting
Because this transfer may be temporary until a local replacement is hired, the family should decide whether to move at all. If they do, the spouse may work for any U.S. employer once in L-2 status and should carry documentation of that status for the employer's records.
Children may attend school. A child near 21 needs a plan for the birthday, since L-2 eligibility ends then and a student category or another basis must be in place beforehand. If the spouse is a Canadian permanent resident rather than a citizen, the L-2 application goes through a consulate rather than a port of entry, which adds time.
If the family stays in L'Ancienne-Lorette and the manager commutes for blocks of weeks, they may visit as visitors, who cannot work or study full time. Whichever plan is chosen, write it down next to the manager's expected duration so that a posting that extends from one year to three does not leave the family's arrangements unexamined.