which bike would you choose?
 

two choices because it's the only two brands the local lbs has to offer.
Which one would you buy? a Trek 520 or a Cannondale Touring 2?

Not that I really know what I'm talking about when it comes to touring bikes, but given that the Cannodale is aluminum, I'd only go with that if I was a bigger guy. I think they are similarly spec'd otherwise? If anyone can make an aluminum tourer it would be Cannondale and several people here have spoken highly of them, so you'd probably be OK. I'm 5'7" and 145lbs, so aluminum scares me.....

Where are you going to ride it?

I've had both Cannondale Aluminum bikes (T1000) and Trek 520. I like the ride of the Cannondale better and had ridden it across the US (twice) and across Canada (once) and a bunch of other places. While riding the perimeter of Australia, I had the frame crack and so I picked up my other Cannondale T1000 to complete the circumference. After that for my next big trip, across Russia, I rode a Trek 520.

So for most cases, I would pick my Cannondale because I like the ride better. If I do a more extended third world tour, I'll take my Trek 520.