Sizing a 29er for off-road touring

[geegee]

I'm thinking of getting a 29er mountain bike to add to my growing stable of bikes. There's a great network of ungroomed rail trails out where I am and I'd like to tour more of the Trans Canada Trail in the future which is mostly off-road and unpaved.

A question to those who tour on 29ers: did you size it as a mountain bike fit (upright riding) or get a slightly larger so you're a bit more stretched out?

I'm looking at a Gary Fisher Ferrous 29. Seems like an awesome steel framed bike perfect for my intentions. I am also thinking of getting an Extrawheel trailer to use with it.

[Successor to the Professor]

With a 29er, you want to be more upright.  You may end up moving down a size when switching over to a 29er since the larger wheels move the frame up (I ride a 16" 29er, and an 18" standard mountain bike), which puts you in a more upright position.  The shorter top tube and wheelbase you get from sizing down works in your advantage by giving your snappier handling that is otherwise lost with the larger wheels.