Power wheelchairs are usually able to go into the wheelchair accessible lines, even when
ECVs are not. Power wheelchairs are usually more manouverable and have a 'footprint' that is closer to a manual wheelchair than most ECVs are.
If a transfer to a manual wheelchair is needed for a line, there will be an attraction wheelchair to switch to. But, the attraction wheelchair will usually not have swingaway armrests or footrests, which some people need to transfer.
I agree with KPeveler that Soaring is likely the easiest transfer.
All are potentially doable. I thought you might like a reminder about Soarin since I have good pictures for it.
Soarin' has a lot of space for transfers and you can park the wheelchair wherever it would be best. If you need something specific, like to park your wheelchair at the start or end of the row or want to be in the middle, let the CM who is assigning people to places know.
TOT has hard metal seats, with several tiers of seats, each tier is up one step.
The door to get into the seating area is fairly narrow and the seats are on either side of a narrow central aisle. There is not room to get the wheelchair into the aisle, from what I remember (someone else who has done it more recently may be able to tell you more).
I don't know who these people are, but their picture gives a good view of the seat arrangement, the tiers and the size of the aisle.
The boarding area is in a different place than unloading. After the guest has transferred into the ride car, a CM will bring the wheelchair to the unload area.
I don't have any pictures of the inside of Star Tours, but the seats are kind of standard theater type seats. A guest using a wheelchair can park the wheelchair very close to the ride seat to transfer over. At the end of the ride, a CM will bring the wheelchair back to transfer back into it.