Decide your use case: sandwiches (crisp + sliceable), bruschetta (chew), or soups/spreads (tang + sturdy bite).
Choose the closest match from the ingredient list based on crust and crumb (French bread for closest all-around, ciabatta for chew).
Use a 1:1 swap by weight or by slice count; if your swap is softer (whole wheat bread), toast longer to firm it up.
Re-crisp crust substitutes: toast in a hot skillet or oven at 425°F (220°C) for 3–5 minutes before serving.
Adjust seasoning: for brioche add salt/garlic to balance sweetness; for sourdough keep toppings simple so tang stays bright.