n.
an imitation nipple used to soothe babies and toddlers; a dummy, a pacifier.
Though COD-2 (s.v. "soother") marks the term as both Canadian and British, internet search results indicate that dummy and pacifier are the more prevalent variants in Canada (see Charts 1, 2 & 3). As Chart 1 shows, soother appears to be, together with Britain, the least prevalent in Canada, while dummy is very frequent in the .ca domain (Chart 2), as is the originally American term pacifier.
See also COD-2, s.v. "Soother"(1), which is marked "Cdn & Brit".