Yes, each day gets a random set of tours for you to play.
Weirdly enough, this doesn't seem to be affected by time-travelling. If you go forward and then back, the souvenirs will have changed but the options for tours will not. Or maybe it's just me/my town.
i actually went into the tuna tour, but didn't start it. i left my ds on through the night, and i just went and picked it up again, and it was still on the tuna kahuna, as expected, but it was nighttime and played the night music?
and when i exited the tour they all were changed but the souvenirs were the same, so..