I'm going to suggest something a little different....I had a toddler once who would not tolerate a stroller or a harness (how you say? well, he'd just sit down!)....and suggest that you give your toddler plenty of opportunities to run. My harness refuser also taught me that the quickest way to create a stroller refuser is to force it. Of course at 6 he'd be happy to ride around WDW in a comfy stroller...lol.
My kids were/are generally happy being carried, so I keep a sling handy so my arms don't get too tired and otherwise let the child do what s/he's happy doing. I do stay close by...the more crowded the situation the closer (ie. at WDW most places would require something akin to hovering).
There are places in WDW where there is some free roaming room and I would definitely take every opportunity to let the little one stretch those legs. When crankiness or stroller refusal hits...high tail it off to someplace for a run. This will serve two purposes....tiring out the little one so s/he's more likely to want to rest in the stroller and showing the little one that you can be trusted to recognize when s/he needs to move...that urge is just so strong with these tiny ones whose legs are getting stronger and faster by the day, it is a need, not just a want.
Of course there will probably be situations that arise that won't allow for immediately heading off for a run....when this happens I usually try to give my toddler as much leeway as possible, even if its a "run 3 steps, back in mom's arms, down for 3 more steps". And there may be other times when you just have to use distraction....handing the child something to focus on while popping into the stroller (since its vacation a lollipop might work...I don't advocate this as an everyday approach!)
There is a sling that can double as a harness, too. It's a Maya Wrap (www.mayawrap.com)....nice and light and no padding. Just an idea so that you have more options.
Be creative, be flexible, and have fun....the keys to life with a toddler! My own toddler will be...um...almost 23 months on our next trip. Should be fun!
Lesley
1979 Contemporary
1992 Off-site
1994 Carribean Beach
1999 Fort Wilderness and Coronado Springs
2000 Polynesian and Old Key West
2002 Boardwalk Villas