Looking at B&H Photo's site, I see they sometimes have two versions of a lens listed; a USA model and an "imported" version that is usually a little cheaper.
What is the difference between the two?
USA models are imported by Canon North America carry a USA/Canadian warranty. The Gray market models were imported by a different Canon division into a different country and do not carry a US warranty. They may not have a English Manual, but most of the lens manuals are multi lingual. The CD/DVD manuals may be multilingual too.
However, if you bought your gray market lens from a authorized Canon distributor like B&H, Canon USA has been known to honor the warranty. If you buy them from a non Canon USA authorized distributor, you will have to deal with your seller to get a warranty. Some provide a third party warranty.