When to use [time of day]+饭 vs [time of day]+餐?
Informally in daily life, we talk about eat meals by referring to 吃饭。 In a formal situation, i.e. hotel, meeting, we use 餐 mostly in writing. 
饭's meaning is quite flexible. You can use 饭 to refer to a general meal. However if you talk about specifically what in the meal, 饭 should be used only for boiled rice. 


我想吃午饭。 ---> A general meal

我今天午饭吃了米饭和汤。 ---> food you eat in a general meal

In Cantonese, they use 餐 referring to a general meal, 饭 for the boiled rice