Since it's in Waldo's nature to be elusive, he won't be leading you on any actual journeys, like Mario did. Instead, when you see him peaking at you, press the play button, and you'll be "transported to places all around the world," as Google claims. From there, you can search for Waldo and his friends in different settings, just like you did when you were a child and didn't have a smartphone or any credit card debt.
There aren't any real rewards for finding Waldo, only what Google describes as "wonderful and wacky badges," that you can show your friends with a questionable degree of self-confidence.
There's not really much to indicate how this qualifies as an April Fool's joke, aside from the fact that Waldo is hard to find, and Google Maps is meant to help you find things. Then again, it's better to play it safe on this specific day of capers.