As I (and others) have stated previously, the location and operational status of Canon's plants is not the only concern. Canon products are assembled at Canon plants, but the parts come from both Canon plants and other vendor plants. Many silicon chip makers have plants in the Sendai area that were obviously affected more than some Canon facilities. If Canon sourced parts from those vendors for lenses and/or bodies, that will impact Canon's production lines.
It's interesting that Canon recently stopped stamping date codes on some lenses. I do know that my 70-200mm f/2.8L IS II, bought soon after the lens was released, has a date code - more recent copies of the lens reportedly do not, so they dropped the date code in production. But, lenses I purchased late last year (35L, 135L) had late 2010 (UY10) date codes, and that means they were produced after Canon stopped putting date codes on the 70-200 II. Does anyone know if this change applies across the board? If Canon does retool another factory for lens production, without the date code initial letter, there may be no way to know where the lens was made (hopefully, it won't matter, but you never know...).