I took a look at Apple’s site for where they are collecting data for maps. Should give us an idea of what to expect.
Andorra, Belgium, Germany, Italy, Spain, Finland, Monaco, Netherlands, Norway, Portugal, San Marino, Singapore, and Sweden. All have completion dates in 2020 or earlier (except Singapore and Italy which completed in January 2021) and have yet to be released.
Currently ongoing are listed as: Australia (until May), France (until April), Israel (until March), New Zealand (until March). They are also doing another tour of the US for all of 2021.
Given what’s been completed, there are quite a few opportunities for what could be next. If I had to guess what Apple might announce at WWDC, I’d say it could be any of the completed ones (with Italy, Spain, Belgium, and maybe Singapore being the most likely in my opinion) and then from the “in progress” list maybe throw in Israel and New Zealand. France and especially Australia’s completion dates I would say are too close to WWDC for Apple to be comfortable announcing it. Israel and New Zealand are both pretty small and Apple could work through their data pretty quickly.