for rough calculations, you can consider the pirogue to be essentially two triangles, with their bases at the center and their apexes at each end.
So a 14' long by 2' wide pirogue would have a bottom footprint (assuming a 1 ' cutback at each end) equal to two triangles,each with a base of 2' and an apex of 6'. That equals a footprint of 12 square feet so sinking the pirogue that first inch in the water would displace one cubic foot or 62.4 lb. As you sink farther displacement increases since the pirogue is flared out at the ends and the sides.
You may want to consider a skiff for your application since it offers a larger footprint than a similar sized pirogue. Beekeeper has a pic on one of his posts showing the difference in bottom footprint of his skiff vs. a pointed end pirogue.
Having said all that, a lot depends on you and your pasenger's skill level in the waters you'll be traveling. Here's a little 14 footer going up Bayou Teche with three hefty riders. Of course this isn't their first pirogue ride