Since AIX on a POWER processor is big-endian and a Linux-based Exadata database node is little-endian, the data blocks are physically different. This means that you cannot use an Oracle Data Guard physical standby. However you can use logical replication like Streams, or GoldenGate (thanks to robinsc for pointing out that even Data Guard SQL apply won't work here).
Can you share some of the configs you're using for datapump? One thing in particular to look for is if you're using doing it in parallel, and if you're using network links.
Other options to improve performance might involve using direct-load inserts over database links (though parallelization is a bit trickier here), or using something like Steams or GoldenGate for continuous logical replication, reducing any actual downtime period.