You can select any arbitrary tile. The opposite corner tile, or any random one in the edge if it's a maze you need to traverse.
This is a maze generator, not a solver. Once the maze is created, you decide where the starting/end points are.
The "flooding it with colour" link leads to an algorithm which will identify far away parts of the maze. You might, for example, pick a faraway (in travelling distance) point that is also on the other side of the maze physically.