SSIS includes two really sophisticated matching transformations in the data flow. The fuzzy lookup transformation is used for mapping the identities. The fuzzy grouping transformation is used for de-duplicating. Both of them use the same algorithm for comparing the strings and other data.
Identity mapping and de-duplication are actually the same problem. For example, instead for mapping the identities of entities in two tables, you can union all of the data in a single table and then do the de-duplication. Or vice versa, you can join a table to itself and then do identity mapping instead of de-duplication. This recipe shows how to use the fuzzy lookup transformation for identity mapping.