No. Derivative status for the transfer routes is available to a legal spouse and to unmarried children under twenty-one. An unmarried partner is not a spouse for this purpose.
Common-law arrangements do not create derivative status
This surprises households whose provincial law treats their relationship as equivalent for property, benefits and taxes. Immigration derivative status turns on a legal marriage recognised where it took place, and a common-law or domestic partnership does not qualify, however long standing and however documented. The practical consequences are stark: the partner would need a status of their own, which for a visitor means limited stays without work permission and no path to live there indefinitely. Households in this position generally either marry, which is a personal decision with legal consequences beyond immigration and should not be made casually for a visa, or they reconsider whether the assignment works at all. The same rule applies to a partner's children, who are not stepchildren without a marriage.
Hypothetical example: a dairy-genetics laboratory transfers a specialist whose spouse is a licensed practical nurse. Their first review produces the marriage record, the expected L-2S documentation and a separate checklist for the nursing licence in the destination state. The spouse's authorization derives from the appropriate L-2S admission record, while the state board controls the clinical work. They should not accept an assignment date until both tracks are visible. If the relationship is not a legal marriage, the partner needs an independent status plan; shared finances and a long history do not replace that requirement.