SURFACE BLEND OF DIFFERENT CONTOURS

Post your model and what version of Creo you are using.

Is this what you need shown in red? I used your existing geometry to create this by extending the swept blend shape into the "U" and then trimming it using the intersection curve present on the "U" channel. I had to use Creo 11 as I do not have 10 available but the picture shows how to do it.

On a side note, if this is intended to go to production there are some issues with some of the sweep trajectories and sections bending too sharply. The geometries are less than optimal for fluid flow and may cause downstream issues with the CAD model. What would be the method of manufacturing these channels?

Depending on how you will make the part with the channels you may have much more flexibility with the geometry you can use for this type of design. Don't constrain your thinking to straight pipes and elbows if that is not actually a manufacturing constraint.

Here is an example of a liquid cooled manifold design for the cylinder head of a single cylinder of an internal combustion engine. This geometry is a closed quilt representing the fluid volume inside a cast part and was used for CFD and thermal analysis to optimize the performance of the cooling component. Once the cooling performance was satisfied by this geometry then a solid shell was built around this control volume for an aluminum sand casting to create the parts. 

For designs that have a primary function of fluid handling or thermal management using fluid containment in a control volume, I would design them from the inside out when possible.