I think for some rides, they ask if you can stand/walk because they need to know if you can get out of your chair or if they need to use the ride vehicle that can accommodate a wheelchair. For the rides without a wheelchair car, some are definitely easier than other. Just as a point of reference, my DD (teen) uses a manual chair and can transfer pretty easily, as her upper body strength is okay.
Also, are you interested in roller coasters? Some of those can be more complicated. One more note...sometimes you have to tell the CM that you need to wait for the special car.
MK
Haunted Mansion is fine...the "doom buggy" has a cut out side to slide over.
DD thought Snow White was tricky. Also, we tried Pirates but don't ride that anymore.
I think Big Thunder was fine. We don't ride Splash. Space Mountain is REALLY hard and complicated. DD is too old to even consider Dumbo, but for rides like that I think the Aladdin ride has a wheelchair accessible vehicle.
Epcot: Spaceship Earth is okay (as described here).
Test Track was okay for DD but it's more than just a slide transfer.
DHS
Rock n Roller Coaster is a little tricky but it also has a sample car to look at.
Tower of Terror was okay for DD but it's NOT a slide transfer.
Star Tours has a seat with a cut out (or the old one did, at any rate).
AK
Everest has a special car for transfers. It's a fairly easy one.
The safari ride allows you to stay in your chair, but I will note that you have to keep an eye on where the CM hooks the tie downs to the wheelchair. They always seem to want to tie down DD's chair on the footrests rather than the frame, which isn't safe.
Hope you have a great trip!
Mary