Every time we've been in Loreto I've seen sea kayakers moving along on the Sea of Cortez. I heard it's fun, but haven't yet it tried it. Here's a company that organizes Sea Kayaking trips:
Sea Kayaking Tours
http://www.tofino.com/baja_sea_kayaking_tours.htm
Check out the pages above, you'll see the different options and a few pictures of the Sea kayaking tours.