Timberpeg sells wall packages that are very similar to what you describe.
They recommend a 6 ml plastic vapor barrier between the t&g and the foam insulation, with all seams lapped and sealed. In my own TF project, I used 6 ml plastic on the walls, but Grace Ice and Water Shield as a vapor barrier above the ceiling boards. This was much more expensive, and overkill really, but I needed a temporary roof and found the plastic was nearly impossible to walk on.
I was not too concerned about trapping condensation against the back of the t&g because I figure it still can dry to one side (the inside) and the foam will keep the vb warm. We are not talking about a stud frame cavity (with its many opportunities for air infiltration) in which collected moisture trapped by the vb could cause unseen rot. In a high moisture area (such as a bathroom), in some climates, maybe a plastic vb against the t&g could cause problems especially if the foam insulation is not staggered and well sealed at the seams.
By the way, this "wrap and strap" system can be hellishly labor intensive.
Unless it's a small DIY project on a tight budget, I'd try to avoid it and go with SIPs.
