The 2014 R3 Shenandoah Epic Adventure Race website gives some basic clues about race composition in the thin description below. The bread and butter disciplines are all there with paddling, biking and orienteering (trekking with nav).
Description: This years race will feature a long paddle to start the race, a day time orienteering course, a day time mtb course followed by a rogain style night course with biking and a night orienteering course.
As for the percentages spent at each discipline, we can only guess. An important question is what, in the Race Director's mind, constitutes a "long paddle". We will be looking to previous race descriptions to see what this RD likes to put together as well as reading the race reports for how the racers felt about old courses. RDs often take feedback from previous years in consideration when designing a course.
Here is a plausible breakdown, focusing on the paddling slice of the pie. It would not be unheard of to put 6 to 8 hours of paddling at the front end of a race. It is however unlikely that the boats will be waiting for teams by the waterside, ready to go at the start of the race. It is all too tempting to send racers over a mountain pass while carrying their canoe and extra gear for good measure.
At any rate, "long paddle" means putting in a solid slice of training either directly paddling a canoe or other vessel, or at least putting a few hours/week in on a rowing machine.
We will be recommending exercises in the training plan for specifically building paddling strength and endurance. Pecs, lats, shoulders, triceps, biceps and core/torso exercises are a staple.