How feasible is is to visit Disneyland and the Redwoods in a 3-4 day trip?
I hate to sound like a former President, but I think it depends on what you mean by "redwoods," and what you mean by "3-4 days."
If, by redwoods, you mean Redwood National Park (
www.nps.gov/redw) or other redwwod forests in Northern CA, you're talking about a
very ambitious trip. Redwood NP is almost on the border of Oregon, and a very long way from Anaheim. The Coastal Redwood range is along the coast (oddly enough) from about the Monterey Bay area north.
If you mean "big trees" then there are actually bigger trees closer in Sequoia/Kings Canyon NP (
www.nps.gov/seki) and Yosemite NP (
www.nps.gov/yose). Both are in central CA, with Sequoia being east of Fresno and Yosemite a little further north, east of Merced.
The Giant Sequoia range is inland, in the Sierra Madre Mountans from about Sequoia up to Gold Country north of Sacramento. If you look on the SEKI site, under Directions, you will find a map showing the ranges of both types of trees. Both are spectacular, but very different ecosystems.
If, by 3-4 days, you mean 4
full days not counting your arrival or departure days, you would have time to see some things but I certainly would not do it that way. You're going to miss so much more than you'll see that I wouldn't consider it worthwhile.
I would do a Southern CA trip, or a Northern CA trip...and I've been to both numerous times and wouldn't bother with Southern CA. But that's me personally -- if you haven't been there, done that, there is a lot to see and do in both places.
Any big tourist stops between them that I chould see?
Only about a thousand. California has virtually limitless "not-to-be-missed" places.
I will have to fly accross the country.
Big benefit going out; big PITA coming back, unless you can sleep on airplanes and take a redeye (I can't).