This info is based on totally free-ranging domestic geese on a saltwater river. They lived on grass; whole corn; bird seed such as millet and milo; oats at times; lettuces, watermelon and cantaloupe; and less expensive Purina cat food, such as Indoor Cat Chow, year-around. They all lived to be at least 20. Not the type of diet those with pet geese usually feed, but just some extra suggestions if chicken feed doesn't work out. Cat food has more protein than geese need, but it seems to work out fine as long as it's not the only thing they eat. If your local feed store has limited options, it doesn't look like you have that many options in Canada for affordable shipped waterfowl food. You don't have Chewy.
P.S. They used plain dirt as grit and got some oyster shell grit during the spring and summer, if they wanted it. And they always really wanted some fresh bread year-around, and it didn't hurt them a bit. They had no shelter, but temps never got below high teens on winter nights.