This is an interesting question.
As guinea pigs are so low to the ground I think it would be pretty rare to clearly see a wee.
However we had one girl (Lucy) who had a favourite corner platform she used to sit on in the C&C.
We had multiple corner platforms, but for some reason this one was the favourite, so once Lucy got up there she tended to stay for a while to stop Harry getting it.
When she wanted to wee she would back herself into the corner, lift her butt up and pee in a perfect stream out of the cage! It truly was extraordinary and I tried many time to get it on film, but never succeeded.
She did it a lot based on the pee all over the floor (the C&C was on a table in the living room).
So based on my observations in one guinea pig I would say they pee in a stream to start, and towards the end it slows and ends with a few small drops.
I am assuming that normal peeing, as opposed to spraying annoying boars (which Lucy also did a lot!) is different.