Belinda: >>nowhere in the poster's question is Paris. She wants to go to Belgium. Not Paris. <<

Huh?????

Did you even read the OP through?

>>Is it worth trying to see Paris instead of Bruges or Brussels?<<

Sorry, I didn't read it carefully enough.

Gretchen has a great idea, if your flights are not already booked. If you decide to go to Paris, you might head there after the wedding, then work your way North to Belgium, then London again to finish up and leave from there.

Brugge is a charming town that you could do in a day.

Weather is unpredictable, and March can be blustery, or windy and rainy, even snowy. I would not enjoy Bruges so much under those conditions. Since Paris has so much to offer even in less than ideal weather, I would choose Paris.