A birthday cake in French is 'un gâteau d'anniversaire'
you have a birthday cake
"la grand-mère sert le gâteau d'anniversaire"
Gateau is food cake in french
Canadians (for the most part speak English) so a birthday cake would be called a birthday cake. However, for the francophones (french speakers) in Canada a birthday cake would be called: gâteau d'anniversaire
gâteau
a birthday is 'un anniversaire' in French
A banana cake is "un gâteau à la banane" in French.
Birthday is "anniversaire" (masc.) in French.
gâteau sucré
d'anniversaire
Joy I see, happiness, laughter and cake... a happy birthday you will have.
If you mean a slice of cake it is - tranche