He wants to go somewhere he is familiar with, so he has an internal map of the place in his head. He also doesn't want to be in the situation where "the extrovert has gone all shy, leaving me to do the communication."
This means that we need to go somewhere where the primary language is English, so I'm not reliant on him to manage a language I've mostly forgotten or never learned, and that we've been to before. The existing stipulations of somewhere with a lot of vegan food that is easy to navigate by public transport using a wheelchair and that has bears somewhere that he can go off and commune with still apply.
This greatly reduces the number of cities quite hilariously:
New York? We both know our way round Manhattan, but unless something's changed in the past few years, it's a nightmare to navigate in a wheelchair - they have a ridiculously small number of pre-book only accessible taxis.
Boston? Lots of vegan food, and I've been there in a wheelchair before. A couple of times, even. Not sure about bears, though.
Toronto? Lots of vegan food, and it seemed that a lot of public transport was accessible in 2007 even before I needed that much accessibility. Also Canadians are very polite and helpful so I wouldn't feel awkward asking for help if I needed it. And Toronto Zoo has THREE (3) types of bear. Flying there is damned expensive though.
Somewhere in the Netherlands or Flemish Belgium? Okay, the primary language there might be Dutch, but pretty much everyone speaks enough English to deal with tourists. I'm looking at Antwerp right now because it's easy to get to (Eurostar plus half an hour, and the second train is included in the price of a Eurostar), and it has a good zoo and art museums, although the zoo does only have one type of bear.