I used that white glue called canopy glue or originally R/C56 which you get at the hobby shops.
It looks like ordinary white aliphatic resin glue but smells different.

I started by putting the fuselage on its side and smearing the glue onto the wood inside where the window would go. Then I dropped the window in place ans squished it down to make good contact all around.
Some glue may squeeze out. Leave it alone. If you try to remove it, the plastic window will be etched and damaged. Once dry however, you can rub it off or cut it at the edge of the window frame to remove any excess. It will come off as though it was never there, leaving no trace.

Since there is poor exposure to the atmosphere, it takes about a day to thoroughly dry. When it is dry, you will see that it is clear and no longer white anywhere. If you see some white, it's still not completely dry.

Then I turned over the fuselage and did the other side.

For the windscreen, I taped it in place while the glue set up.

Took several days but since it took seven years for me to complete the plane, there was no hurry and a few days was really fast.

I suppose you could also use instant glue. However, that can be quite messy and can craze the plastic. Then it's a big problem to fix. With the canopy glue, you can also easily remove the windows for repairs.