Yu never really know what you would do in that situation but my first thought would be to paddle backward towards it hoping somehow he would not get up the momentum to swallow me whole or be so overcome with curiosity he would give me a fly by and let me escape to shallow water.
Once he made aggressive contact I would be making my best Mark Maguire/ Sammy Sosa impression and swingin for the fence!
"Industria, Virtus, et Fortitudo"
(means build it right, ride it hard, and never let up!)
Just Like lightning, only faster!