Just trying to clarify...
I guess the original circuit can be simplified down to this:
View attachment 18665
Do you agree with that diagram?
Then the power dissipated in each current source can be calculated using the Power law, taking into account the direction of current flow.
So you guys are assuming that the arrow in the current source represents the direction of conventional current flow? AFAIK that's true; I've never seen a current source where the arrow direction represented electron flow.