Any power-modifying effects, counters, Auras, or Equipment will apply after Evra's power is set to your former life total. For example, say Evra is enchanted with Dub (which makes it 6/6) and your life total is 7. After the exchange, Evra would be a 9/6 creature (its power became 7, which was then modified by Dub) and your life total would be 6.