A recent and readable book by Tom Koppel, 1995, "Kanaka, the Untold Story of Hawaiian Pioneers in British Columbia and the Pacific Northwest," was published by Whitecap Books. The book (paperback) has photographs and stories of the settlers, whom Koppel mostly characterizes as "gutsy survivors." The bibliography is good.
The number that came over will never be known; many came on their own, without contract, or hired on ships calling at the islands and in need of crewmen.