It can be red, white, or even sparkling wine (such as 'Crémant', less expensive than Champagne, white or rosé). The choice will affect the taste of the soup, so it's better to know whether the persons you intend to serve the soup to will like this kind of wine. There's no known to be the best wine, there's the one your guests/you like :)
You can then make the soup accordingly, and adapt the type of wine/strawberry/ingredients you use (lemon ? mint ? cinnamon ?...)
The bitter the strawberries, the sweeter the wine is a kind of good rule AFAIK.
If not using wine, I've had a really good experience with a blackcurrent cream (6/8°). It came from Burgundy/France. It gives a more sweet, and a little more thicker soup. It can be use alone, or mixed (40% to 60 % or +/-) with red wine.
Pinot noir is my favourite, but @Ken already gave you some good tips about wines (Muscat, Chardonnay, Pinot, Asti, Gamay...) so I'll focus about the if my recipe could be improved somehow part of your question.
I made soups with a couple of freshly cut mint leaves in it (feels really refreshing then). You can also add cinnamon, or vanilla, or ginger in the wine when you heat it (but I recommand not to use any two of them at the same time and mixing).
A tiny lemon juice (some drops) over the strawberries also adds some refreshing taste.
Instead of the toasted bread, little cubes of cinnamon bread is good too (but then, no cinammon in the wine when heating, otherwise, it's too much of it).
No strawberries ? any fruit like raspberries, peaches or cherries can do it too...