I'll throw something a bit different into the arena - various of the pacific north-western indigenous peoples were actively raiding along the pacific coast in the 1850's so they could also be a possible opponent.
From wikipedia
"Chilkat Tlingit warriors attacked and burned Fort Selkirk, the Hudson's Bay Company post at the juncture of the Yukon and Pelly Rivers, in 1852. The Chilkat had been middlemen between the company and the Athapaskan people of the interior (on preexisting trade routes), and were unwilling to be excluded from the arrangement.
In 1855, an alliance of Tongass Tlingit (Stikines) and Haida raided Puget Sound on an enslavement expedition. Confronted at Port Gamble, Washington Territory by the USS Massachusetts and other naval vessels, the raiders suffered casualties, included a Haida chief. A return expedition by the alliance the following year was punitive, with Isaac N. Ebey chosen at random as a high-ranking white man whose death would avenge the chief's death the previous year. Although the territorial government pressed the colonial government of Vancouver Island to apprehend Ebey's killer, the colonial authorities lacked a sufficient military capability to mount an expedition capable of defeating the Haida-Tlingit alliance, and Ebey's killer was never identified or captured"