My sister was recently stranded in DFW trying to make it to SFO when American Airlines canceled her flight. They were happy to substitute another flight... to Sacramento.
So the two-hour round trip to pick her up from SFO turned into an eight-hour round trip to Sacramento. I'm amazed this was considered an acceptable substitute. Would have been nice if American was willing to get you home in the event of canceled flights.
(We could see available seats on flights from DFW to SFO at that time from Delta and Alaska. But those seats were "not available to American rebooking agents". It seems like that should have been American's problem, not ours.)
Footnote: even though my sister had to be rebooked onto the American flight to Sacramento, American didn't bother rerouting her luggage, which they sent to SFO. I guess canceling the flight meant "the plane will still fly, but without passengers".