UPDATE D
SET
	[MyColumn1] = S.[MyColumn1],
	[MyStringColumn2] = S.[MyStringColumn2],
	...
FROM	dbo.MyDestinationTable AS D
	JOIN dbo.MySourceTable AS S
		 ON D.[MyPKColumn] = S.[MyPKColumn]

WHERE
	(
		   (D.[MyColumn1] <> S.[MyColumn1]
			OR (D.[MyColumn1] IS NULL AND S.[MyColumn1] IS NOT NULL)
			OR (D.[MyColumn1] IS NOT NULL AND S.[MyColumn1] IS NULL))
		OR (D.[MyStringColumn2] COLLATE Latin1_General_BIN <> S.[MyStringColumn2]
			OR (D.[MyStringColumn2] IS NULL AND S.[MyStringColumn2] IS NOT NULL)
			OR (D.[MyStringColumn2] IS NOT NULL AND S.[MyStringColumn2] IS NULL))
	)