In northern climates it is a big issue. I'm not sure we really understand the science of it. Where I live even the location of the vapour barrier is in review. I've seen several different routes for sealing joints between different materials on details where new and existing buildings joined.

These are what I view as the issues that need to be addressed with the joint
-the outside needs to keep moisture out
-the vapour barrier needs to be located in the correct location for your climate
-any vapour that does condense needs to have an escape out of the wall.
-the joint has to accommodate for movement in the timber.

I think if you are set on having timbers exposed on the inside and the outside you are on the right track with the expanding foam strips.

Another question is how do you plan to heat this home? Might a breathable wall infill made of log or straw better suit your needs? There are also wood fiber and OSB SIPs available near you.