Most of our merchant partners offer open denominations, but some (e.g. Hudson's Bay) only offer fixed denominations ($10, $25, $50, $100, $250, $500). The sender is notified when choosing a denomination which merchants are not available as redemption options.
The merchants showing for your gift are the ones that are available to choose from for your gift denomination.
The recipient also has the option to split the gift between multiple different merchants if they wish to do so.