I had the same problem on the sword I created from scratch in MilkShape, it looked fine in MilkShape and then was missing triangles when loaded in DBP.
Unfortunately I am not familiar with the tools in 3d Canvas Pro, but first you should figure out how to turn off drawing backfaces in 3d Canvas Pro so that you can see it the way it'll be in DBP. In MilkShape you can select the missing face and reverse vertex order to make it texture the correct side. I should think there would be a similar command.
I hope that helps =)
A Cloaking Robe of Elven-Kind hangs in my wardrobe behind
All those things that mother said were proper for a boy