Cities: Skylines

You actually only need to win one scenario. Save right before achieving the win condition. After you win, return to the main menu, load your save, repeat 5x.

If you have the Mass Transit DLC, the ferry one is extremely easy if you are willing to let it idle. Buy the next square up and build some space up until you get to 25k population. If you replace your dumps and cemetaries with incinerators and crematoriums,
you can just leave it running overnight. Its mostly a matter of how much time you want to spend on setup to speed up the process.

You can place a few canals to connect the starting areas and and then place a ferry depot and a few stations, create paths between them then set up the route.
That should get you about 100/wk.

I also created an office/commercial zone north of the highway, and a residential south of it. They were probably about 4-6 double block wide and 5 or 6 blocks high.
I purposely only connected them to the highway side they were closest to, so it was inconvenient to get from one section to the other by car. I then looped a canal around them, and added some docks and stops. (Don't forget you need to include water (and make a path) so the boats can get from the depot to your loop.)
You will have to redo the highway a bit to take it over the canals. It works best if you come at the call exactly perpendicular, go up one elevation step and get right up to the edge of the canal before trying to cross it. You may need to drag it a ways past the canal to get it to let you place it, and afterwards you can delete the excess and bring it back down to ground level.
This is good for another 200 or so per week.
You can also stick some addition office/industrial/commercial/residential outside the loop and stick some docks and create routes there as well. I ended up getting up to 550/week before I stopped and just let it sit.