Can a Thunder Bay engineer's spouse work in the United States during the lay-up months?

No. TD status permits residence and study but carries no work authorization at any point, and a short seasonal stay does not create a temporary exception. If the household needs a second income while they are in the United States, that income has to come from a status held in the spouse's own right.

What TD reaches, and what it does not

Derivative status exists only while Eero holds his own, and it authorizes no employment of any kind. His spouse could not take a job at the yard, could not freelance locally, and could not continue working remotely for a Thunder Bay employer from inside the United States. Two further points matter for a household that moves back and forth each season.

The relationship has to be a legally recognized marriage, because a common-law partner is not a spouse for these purposes and would need an independent route. A child stops qualifying as a derivative at twenty-one, which for a family that repeats this pattern for several winters is a date worth writing down now rather than discovering at the border. Where a second income is essential, it is worth comparing the L-2 and E-2 spouse rules, under which a spouse is employment-authorized incident to status.