I've been vegan for a number of years and manage to be fed in Paris, Bruges and Amsterdam! It IS helpful that restaurants have menus posted outside so you can check to see what might work for your group before you go in. For breakfast in Paris I generally just have baguette at the hotel.
I don't eat high end - just me traveling solo and I'm not that in to food.
I have used Happy Cow some but also find others. I did have some on my list last time but never got to them. They are Hank Burger and Le Potager Marais. I've added them to my list for next time.
My fall back is falafel, lol but I love it and live in an area where there is very little ethnic food. I love Mi-va-Mi in the Marais which is right across the street from one of the big names in falafel - L'As du Fallafel. I like Mi-va-Mi better, not as crowded, staff is very nice and it always looks like "Mama" is on the cash register. You do need to be mindful of Saturday closures in the Marais district as it is the Jewish quarter. I also love a small fast food stand called Maoz which serves very good falafel pitas. The one I like is on Rue Saint-Andre-des-Arts in the Saint-Germain-des-Pres area. I used to make sure I got a sandwich from a chain called Hure (accent over the e which I can't get to right now, lol) when I was near Notre Dame. They have a very nice veggie baguette with no butter on it. I'll still go by and see if I can give them some business as I am sure they are suffering with business decline.
I also like another chain called Le Pain Quotidien altho they are a bit pricier. They always have vegan selections.
If I'm stumped I will just head for an Italian place and get pizza or pasta.
There is a wonderful chain of gelato stands called Amorino. They have a number of flavors of sorbetto and they mark their vegan ones for you. There is one near the hotel I usually stay at but it does not have as many flavors as the one at the Place de la Concorde end of the Tuileries near the Orangerie Museum. My favorite flavors are the chocolate and banana sorbettos. Delicious!
For Bruges, I was there this spring and had delicious pasta at Trattoria Trium on Academiestraat. I also got picnic stuff at the Carrefour Express just off the Grote Markt. I also found this blog which had good information but I never had time to go to any of the places she suggested!
The Bruges Vegan https://brugesvegan.com/list-restaurants-bruges/
Have a wonderful time! If you discover some good places I'd love to hear about them!